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</div> <div class="control"> <button class="button is-small is-link">Go</button> </div> </div> </form> </div> </div> <nav class="pagination is-small is-centered breathe-horizontal" role="navigation" aria-label="pagination"> <a href="" class="pagination-previous is-invisible">Previous </a> <a href="/search/?searchtype=author&query=Panaitescu%2C+A&start=50" class="pagination-next" >Next </a> <ul class="pagination-list"> <li> <a href="/search/?searchtype=author&query=Panaitescu%2C+A&start=0" class="pagination-link is-current" aria-label="Goto page 1">1 </a> </li> <li> <a href="/search/?searchtype=author&query=Panaitescu%2C+A&start=50" class="pagination-link " aria-label="Page 2" aria-current="page">2 </a> </li> </ul> </nav> <ol class="breathe-horizontal" start="1"> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2209.11847">arXiv:2209.11847</a> <span> [<a href="https://arxiv.org/pdf/2209.11847">pdf</a>, <a href="https://arxiv.org/ps/2209.11847">ps</a>, <a href="https://arxiv.org/format/2209.11847">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> </div> </div> <p class="title is-5 mathjax"> Properties of the Prompt Optical Counterpart Arising from the Cooling of Electrons in Gamma-Ray Bursts </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A+D">A. D. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Vestrand%2C+W+T">W. T. Vestrand</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2209.11847v1-abstract-short" style="display: inline;"> This work extends a contemporaneous effort (Panaitescu & Vestrand 2022) to study the properties of the lower-energy counterpart synchrotron emission produced by the cooling of relativistic Gamma-Ray Burst (GRB) electrons through radiation (synchrotron and self-Compton) emission and adiabatic losses. We derive the major characteristics (pulse duration, lag-time after burst, brightness relative to… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2209.11847v1-abstract-full').style.display = 'inline'; document.getElementById('2209.11847v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2209.11847v1-abstract-full" style="display: none;"> This work extends a contemporaneous effort (Panaitescu & Vestrand 2022) to study the properties of the lower-energy counterpart synchrotron emission produced by the cooling of relativistic Gamma-Ray Burst (GRB) electrons through radiation (synchrotron and self-Compton) emission and adiabatic losses. We derive the major characteristics (pulse duration, lag-time after burst, brightness relative to the burst) of the Prompt Optical Counterpart (POC) accompanying GRBs. Depending on the magnetic field life-time, duration of electron injection, and electron transit-time Dto from hard X-ray (GRB) to optical emitting energies, a (true) POC may appear during the GRB pulse (of duration dtg) or after (delayed OC). The signature of counterparts arising from the cooling of GRB electrons is that true POC pulses (Dto < dtg) last as long as the corresponding GRB pulse (dto ~ dtg) while delayed OC pulses (Dto > dtg) last as long as the transit-time (dto ~ Dto). If OC variability can be measured, then another signature for this OC mechanism is that the GRB variability is "passed" only to POCs but is lost for delayed OCs. Within the GRB electron cooling model for counterparts, POCs should be on average dimmer than delayed one (which is found to be consistent with the data), and harder GRB low-energy slopes bLE should be associated more often with the dimmer POCs The range of low-energy slopes bLE in [-1/2,1/3] produced by electron cooling and the average burst brightness of 1 mJy (with 1 dex dispersion) imply that POCs of hard GRBs can be dimmer than R=20 and difficult to detect by robotic telescopes (unless there is another mechanism that overshines the emission from cooling electrons) and that the POCs of soft GRBs can be brighter than R=10, i.e. as bright as the Optical Flashes (OFs) seen for several bursts. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2209.11847v1-abstract-full').style.display = 'none'; document.getElementById('2209.11847v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 23 September, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">14 pages, to be published in the ApJ</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2209.10014">arXiv:2209.10014</a> <span> [<a href="https://arxiv.org/pdf/2209.10014">pdf</a>, <a href="https://arxiv.org/ps/2209.10014">ps</a>, <a href="https://arxiv.org/format/2209.10014">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/1538-4357/ac8b75">10.3847/1538-4357/ac8b75 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> The Synchrotron Low-Energy Spectrum Arising from the Cooling of Electrons in Gamma-Ray Bursts </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A+D">A. D. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Vestrand%2C+W+T">W. T. Vestrand</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2209.10014v2-abstract-short" style="display: inline;"> This work is a continuation of a previous effort (Panaitescu 2019) to study the cooling of relativistic electrons through radiation (synchrotron and self-Compton) emission and adiabatic losses, with application to the spectra and light-curves of the synchrotron Gamma-Ray Burst produced by such cooling electrons. Here, we derive the low-energy slope b_LE of GRB pulse-integrated spectrum and quantif… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2209.10014v2-abstract-full').style.display = 'inline'; document.getElementById('2209.10014v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2209.10014v2-abstract-full" style="display: none;"> This work is a continuation of a previous effort (Panaitescu 2019) to study the cooling of relativistic electrons through radiation (synchrotron and self-Compton) emission and adiabatic losses, with application to the spectra and light-curves of the synchrotron Gamma-Ray Burst produced by such cooling electrons. Here, we derive the low-energy slope b_LE of GRB pulse-integrated spectrum and quantify the implications of the measured distribution of b_LE. If the magnetic field lives longer than it takes the cooling GRB electrons to radiate below 1-10 keV, then radiative cooling processes of power P(gamma) ~ gamma^n with n geq 2, i.e. synchrotron and inverse-Compton (iC) through Thomson scatterings, lead to a soft low-energy spectral slope b_LE leq -1/2 of the GRB pulse-integrated spectrum F_eps ~ eps^{b_LE} below the peak-energy E_p, irrespective of the duration of electron injection t_i. IC-cooling dominated by scatterings at the Thomson--Klein-Nishina transition of synchrotron photons below E_p has an index n = 2/3 -> 1 and yield harder integrated spectra with b_LE in [0,1/6], while adiabatic electron-cooling leads to a soft slope b_LE = -3/4. Radiative processes that produce soft integrated spectra can accommodate the harder slopes measured by CGRO/BATSE and Fermi/GBM only if the magnetic field life-time t_B is shorter than the time during which the typical GRB electrons cool to radiate below 1-10 keV, which is less than (at most) ten radiative cooling timescales t_rad of the typical GRB electron. In this case, there is a one-to-one correspondence between t_B and b_LE. To account for low-energy slopes b_LE > -3/4, adiabatic electron-cooling requires a similar restriction on t_B. In this case, the diversity of slopes arises mostly from how the electron-injection rate varies with time and not from the magnetic field timescale. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2209.10014v2-abstract-full').style.display = 'none'; document.getElementById('2209.10014v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 6 October, 2022; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 20 September, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">31 pages, to appear in the ApJ, added discussion of broken power-law low-energy GRB spectra, additions are shown in italics</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2005.00104">arXiv:2005.00104</a> <span> [<a href="https://arxiv.org/pdf/2005.00104">pdf</a>, <a href="https://arxiv.org/ps/2005.00104">ps</a>, <a href="https://arxiv.org/format/2005.00104">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/1538-4357/ab8bdf">10.3847/1538-4357/ab8bdf <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> X-ray Afterglows from the Gamma-Ray Burst "Large(r)-Angle" Emission </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2005.00104v1-abstract-short" style="display: inline;"> We derive basic analytical results for the timing and decay of the GRB-counterpart and delayed-afterglow light-curves for a brief emission episode from a relativistic surface endowed with angular structure, consisting of a uniform Core of size theta_c (Lorentz factor Gamma_c and surface emissivity i_nu are angle-independent) and an axially-symmetric power-law Envelope (Gamma ~ theta^{-g}). In th… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2005.00104v1-abstract-full').style.display = 'inline'; document.getElementById('2005.00104v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2005.00104v1-abstract-full" style="display: none;"> We derive basic analytical results for the timing and decay of the GRB-counterpart and delayed-afterglow light-curves for a brief emission episode from a relativistic surface endowed with angular structure, consisting of a uniform Core of size theta_c (Lorentz factor Gamma_c and surface emissivity i_nu are angle-independent) and an axially-symmetric power-law Envelope (Gamma ~ theta^{-g}). In this Large-Angle Emission (LAE) model, radiation produced during the prompt emission phase (GRB) at angles theta > theta_c arrives at observer well after the burst (delayed emission). The dynamical time-range of the very fast-decaying GRB "tail" and of the flat afterglow "plateau", and the morphology of GRB counterpart/afterglow, are all determined by two parameters: the Core's parameter Gamma_c*theta_c and the Envelope's Lorentz factor index g, leading to three types of light-curves that display three post-GRB phases (type 1: tail, plateau/slow-decay, post-plateau/normal-decay), two post-GRB phases (type 2: tail and fast-decay), or just one (type 3: normal decay). We show how X-ray light-curve features can be used to determine Core and Envelope dynamical and spectral parameters. Testing of the LAE model is done using the Swift/XRT X-ray emission of two afterglows of type 1 (060607A, 061121), one of type 2 (061110A), and one of type 3 (061007). We find that the X-ray afterglows with plateaus require an Envelope Lorentz factor Gamma ~ theta^{-2} and a comoving-frame emissivity i_nu ~ theta^2, thus, for a typical afterglow spectrum F_nu ~ nu^{-1}, the lab-frame energy release is uniform over the emitting surface. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2005.00104v1-abstract-full').style.display = 'none'; document.getElementById('2005.00104v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 30 April, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2020. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">16 pages, to appear in the ApJ</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1905.10440">arXiv:1905.10440</a> <span> [<a href="https://arxiv.org/pdf/1905.10440">pdf</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/1538-4357/ab4e17">10.3847/1538-4357/ab4e17 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Adiabatic and Radiative Cooling of Relativistic Electrons Applied to Synchrotron Spectra and Light-Curves of Gamma-Ray Burst Pulses </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1905.10440v1-abstract-short" style="display: inline;"> We investigate the adiabatic and radiative (synchrotron and inverse-Compton) cooling of relativistic electrons whose injected/initial distribution with energy is a power-law above a typical energy $纬_i$. Analytical and numerical results are presented for the cooling-tail and the cooled-injected distribution that develop below and above the typical energy of injected electrons, for the evolution of… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1905.10440v1-abstract-full').style.display = 'inline'; document.getElementById('1905.10440v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1905.10440v1-abstract-full" style="display: none;"> We investigate the adiabatic and radiative (synchrotron and inverse-Compton) cooling of relativistic electrons whose injected/initial distribution with energy is a power-law above a typical energy $纬_i$. Analytical and numerical results are presented for the cooling-tail and the cooled-injected distribution that develop below and above the typical energy of injected electrons, for the evolution of the peak-energy $E_p$ of the synchrotron emission spectrum, and for the pulse shape resulting from an episode of electron injection. The synchrotron emission calculated numerically is compared with the spectrum and shape of Gamma-Ray Burst (GRB) pulses. Both adiabatic and radiative cooling processes lead to a softening of the pulse spectrum, and both types of cooling processes lead to pulses peaking earlier and lasting shorter at higher energy, quantitatively consistent with observations. For adiabatic-dominated electron cooling, a power-law injection rate $R_i$ suffices to explain the observed power-law GRB low-energy spectra. Synchrotron-dominated cooling leads to power-law cooling-tails that yield the synchrotron standard slope alpha = -3/2 provided that $R_i \sim B^2$, which is exactly the expectation if the magnetic field is a constant fraction of the post-shock energy density. Increasing (decreasing) $R_i$ and decreasing (increasing) B(t) lead to slopes alpha harder (softer, respectively) than the standard value and to non--power-law (curved) cooling-tails. Inverse-Compton cooling yields four values for the slope alpha but, as for synchrotron, other $R_i$ or B histories yield a wider range of slopes and curved low-energy spectra. Feedback between the power-law segments that develop below and above the typical injected electron leads to a synchrotron spectrum with many breaks above and below the usual 10 keV-1 MeV observing range. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1905.10440v1-abstract-full').style.display = 'none'; document.getElementById('1905.10440v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 24 May, 2019; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2019. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">19 pages, submitted to ApJ</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1605.09367">arXiv:1605.09367</a> <span> [<a href="https://arxiv.org/pdf/1605.09367">pdf</a>, <a href="https://arxiv.org/ps/1605.09367">ps</a>, <a href="https://arxiv.org/format/1605.09367">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/1538-4357/837/1/13">10.3847/1538-4357/837/1/13 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> The 7.2/3 Years Collection of Well-Monitored Fermi-LAT GRB Afterglows </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1605.09367v3-abstract-short" style="display: inline;"> We present the light-curves and spectra of 24 afterglows that have been monitored by Fermi-LAT at 0.1-100 GeV over more than a decade in time. All light-curves (except 130427) are consistent with a single power-law starting from their peaks, which occurred, in most cases, before the burst end. The light-curves display a brightness-decay rate correlation, with all but one (130427) of the bright aft… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1605.09367v3-abstract-full').style.display = 'inline'; document.getElementById('1605.09367v3-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1605.09367v3-abstract-full" style="display: none;"> We present the light-curves and spectra of 24 afterglows that have been monitored by Fermi-LAT at 0.1-100 GeV over more than a decade in time. All light-curves (except 130427) are consistent with a single power-law starting from their peaks, which occurred, in most cases, before the burst end. The light-curves display a brightness-decay rate correlation, with all but one (130427) of the bright afterglows decaying faster than the dimmer afterglows. We attribute this dichotomy to a quick deposition of the relativistic ejecta energy in the external-shock for the brighter/faster-decaying afterglows and to an extended energy-injection in the afterglow shock for the dimmer/slower-decaying light-curves. The spectra of six afterglows (090328, 100414, 110721, 110731, 130427, 140619B) indicate the existence of a harder component above a spectral dip/ankle at energy 0.3-3 GeV, offering evidence for an inverse-Compton emission at higher energies, and suggesting that the harder power-law spectra of five other LAT afterglows (130327B, 131231, 150523, 150627, 160509) could also be inverse-Compton, while the remaining softer LAT afterglows should be synchrotron. Marginal evidence for a spectral break and softening at higher energies is found for two afterglows (090902B and 090926). <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1605.09367v3-abstract-full').style.display = 'none'; document.getElementById('1605.09367v3-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 10 January, 2017; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 30 May, 2016; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2016. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">13 pages, accepted by ApJ, light-curves and spectra of 24 LAT afterglows are tabulated</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1504.03205">arXiv:1504.03205</a> <span> [<a href="https://arxiv.org/pdf/1504.03205">pdf</a>, <a href="https://arxiv.org/ps/1504.03205">ps</a>, <a href="https://arxiv.org/format/1504.03205">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/0004-637X/806/1/64">10.1088/0004-637X/806/1/64 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Optical Flashes from Internal Pairs Formed in Gamma-Ray Burst Afterglows </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1504.03205v1-abstract-short" style="display: inline;"> We develop a numerical formalism for calculating the distribution with energy of the (internal) pairs formed in a relativistic source from unscattered MeV--TeV photons. For GRB afterglows, this formalism is more suitable if the relativistic reverse-shock that energizes the ejecta is the source of the GeV photons. The number of pairs formed is set by the source GeV output (calculated from the F… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1504.03205v1-abstract-full').style.display = 'inline'; document.getElementById('1504.03205v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1504.03205v1-abstract-full" style="display: none;"> We develop a numerical formalism for calculating the distribution with energy of the (internal) pairs formed in a relativistic source from unscattered MeV--TeV photons. For GRB afterglows, this formalism is more suitable if the relativistic reverse-shock that energizes the ejecta is the source of the GeV photons. The number of pairs formed is set by the source GeV output (calculated from the Fermi-LAT fluence), the unknown source Lorentz factor, and the unmeasured peak energy of the LAT spectral component. We show synchrotron and inverse-Compton light-curves expected from pairs formed in the shocked medium and identify some criteria for testing a pair origin of GRB optical counterparts. Pairs formed in bright LAT afterglows with a Lorentz factor in the few hundreds may produce bright optical counterparts (R < 10) lasting for up to one hundred seconds. The number of internal pairs formed from unscattered seed photons decreases very strongly with the source Lorentz factor, thus bright GRB optical counterparts cannot arise from internal pairs if the afterglow Lorentz factor is above several hundreds. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1504.03205v1-abstract-full').style.display = 'none'; document.getElementById('1504.03205v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 13 April, 2015; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2015. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">14 pages, to appear in the ApJ</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1407.7492">arXiv:1407.7492</a> <span> [<a href="https://arxiv.org/pdf/1407.7492">pdf</a>, <a href="https://arxiv.org/ps/1407.7492">ps</a>, <a href="https://arxiv.org/format/1407.7492">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/0004-637X/793/2/104">10.1088/0004-637X/793/2/104 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Synchrotron and inverse-Compton emissions from pairs formed in GRB afterglows (analytical treatment) </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1407.7492v1-abstract-short" style="display: inline;"> We calculate the synchrotron and inverse-Compton emissions from pairs formed in GRB afterglows from high-energy photons (above 100 MeV), assuming a power-law photon spectrum C_nu ~ nu^{-2} and considering only the pairs generated from primary high-energy photons. The essential properties of these pairs (number, minimal energy, cooling energy, distribution with energy) and of their emission (peak f… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1407.7492v1-abstract-full').style.display = 'inline'; document.getElementById('1407.7492v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1407.7492v1-abstract-full" style="display: none;"> We calculate the synchrotron and inverse-Compton emissions from pairs formed in GRB afterglows from high-energy photons (above 100 MeV), assuming a power-law photon spectrum C_nu ~ nu^{-2} and considering only the pairs generated from primary high-energy photons. The essential properties of these pairs (number, minimal energy, cooling energy, distribution with energy) and of their emission (peak flux, spectral breaks, spectral slope) are set by the observables GeV fluence Phi (t) = Ft and spectrum, and by the Lorentz factor Gamma and magnetic field B of the source of high-energy photons, at observer-time t. Optical and X-ray pseudo--light-curves F_nu (Gamma) are calculated for given B; proper synchrotron self-Compton light-curves are calculated by setting the dynamics Gamma(t) of the high-energy photons source to be that of a decelerating, relativistic shock. It is found that the emission from pairs can accommodate the flux and decays of the optical flashes measured during the prompt (GRB) phase and of the faster-decaying X-ray plateaus observed during the delayed (afterglow) phase. The brightest pair optical emission is obtained for 100 < Gamma < 500, and depends mostly on the GeV fluence, being independent of the source redshift. Emission from pairs formed during the GRB phase offers an alternate explanation to reverse-shock optical flashes. These two models may be distinguished based on their corresponding flux decay index--spectral slope relations, different correlations with the LAT fluence, or through modeling of the afterglow multiwavelength data. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1407.7492v1-abstract-full').style.display = 'none'; document.getElementById('1407.7492v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 28 July, 2014; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> July 2014. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">14 pages, accepted by ApJ</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1311.5867">arXiv:1311.5867</a> <span> [<a href="https://arxiv.org/pdf/1311.5867">pdf</a>, <a href="https://arxiv.org/ps/1311.5867">ps</a>, <a href="https://arxiv.org/format/1311.5867">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1093/mnras/stt1792">10.1093/mnras/stt1792 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> An external-shock model for GRB afterglow 130427A </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Vestrand%2C+W+T">W. T. Vestrand</a>, <a href="/search/astro-ph?searchtype=author&query=Wozniak%2C+P">P. Wozniak</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1311.5867v1-abstract-short" style="display: inline;"> The complex multiwavelength emission of GRB afterglow 130427A (monitored in the radio up to 10 days, in the optical and X-ray until 50 days, and at GeV energies until 1 day) can be accounted for by a hybrid reverse-forward shock synchrotron model, with inverse-Compton emerging only above a few GeV. The high ratio of the early optical to late radio flux requires that the ambient medium is a wind an… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1311.5867v1-abstract-full').style.display = 'inline'; document.getElementById('1311.5867v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1311.5867v1-abstract-full" style="display: none;"> The complex multiwavelength emission of GRB afterglow 130427A (monitored in the radio up to 10 days, in the optical and X-ray until 50 days, and at GeV energies until 1 day) can be accounted for by a hybrid reverse-forward shock synchrotron model, with inverse-Compton emerging only above a few GeV. The high ratio of the early optical to late radio flux requires that the ambient medium is a wind and that the forward-shock synchrotron spectrum peaks in the optical at about 10 ks. The latter has two consequences: the wind must be very tenuous and the optical emission before 10 ks must arise from the reverse-shock, as suggested also by the bright optical flash that Raptor has monitored during the prompt emission phase (<100 s). The VLA radio emission is from the reverse-shock, the Swift X-ray emission is mostly from the forward-shock, but the both shocks give comparable contributions to the Fermi GeV emission. The weak wind implies a large blast-wave radius (8 t_{day}^{1/2} pc), which requires a very tenuous circumstellar medium, suggesting that the massive stellar progenitor of GRB 130427A resided in a super-bubble. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1311.5867v1-abstract-full').style.display = 'none'; document.getElementById('1311.5867v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 22 November, 2013; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> November 2013. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">7 pages, MNRAS, in press</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1311.5489">arXiv:1311.5489</a> <span> [<a href="https://arxiv.org/pdf/1311.5489">pdf</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1126/science.1242316">10.1126/science.1242316 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> The Bright Optical flash and Afterglow from the Gamma-Ray Burst GRB 130427A </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Vestrand%2C+W+T">W. T. Vestrand</a>, <a href="/search/astro-ph?searchtype=author&query=Wren%2C+J">J. Wren</a>, <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Wozniak%2C+P">P. Wozniak</a>, <a href="/search/astro-ph?searchtype=author&query=Davis%2C+H">H. Davis</a>, <a href="/search/astro-ph?searchtype=author&query=Palmer%2C+D">D. Palmer</a>, <a href="/search/astro-ph?searchtype=author&query=Vianello%2C+G">G. Vianello</a>, <a href="/search/astro-ph?searchtype=author&query=Omodei%2C+N">N. Omodei</a>, <a href="/search/astro-ph?searchtype=author&query=Xiong%2C+S">S. Xiong</a>, <a href="/search/astro-ph?searchtype=author&query=Briggs%2C+M">M. Briggs</a>, <a href="/search/astro-ph?searchtype=author&query=Elphick%2C+M">M. Elphick</a>, <a href="/search/astro-ph?searchtype=author&query=Rosing%2C+W">W. Rosing</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1311.5489v1-abstract-short" style="display: inline;"> The optical light that is generated simultaneously with the x-rays and gamma-rays during a gamma-ray burst (GRB) provides clues about the nature of the explosions that occur as massive stars collapse to form black holes. We report on the bright optical flash and fading afterglow from the powerful burst GRB 130427A and present a comparison with the properties of the gamma-ray emission that show cor… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1311.5489v1-abstract-full').style.display = 'inline'; document.getElementById('1311.5489v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1311.5489v1-abstract-full" style="display: none;"> The optical light that is generated simultaneously with the x-rays and gamma-rays during a gamma-ray burst (GRB) provides clues about the nature of the explosions that occur as massive stars collapse to form black holes. We report on the bright optical flash and fading afterglow from the powerful burst GRB 130427A and present a comparison with the properties of the gamma-ray emission that show correlation of the optical and >100 MeV photon flux light curves during the first 7,000 seconds. We attribute this correlation to co-generation in an external shock. The simultaneous, multi-color, optical observations are best explained at early times by reverse shock emission generated in the relativistic burst ejecta as it collides with surrounding material and at late times by a forward shock traversing the circumburst environment. The link between optical afterglow and >100 MeV emission suggests that nearby early peaked afterglows will be the best candidates for studying GRB emission at GeV/TeV energies. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1311.5489v1-abstract-full').style.display = 'none'; document.getElementById('1311.5489v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 21 November, 2013; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> November 2013. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Main text and supplementary materials that will appear in Science</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1308.3197">arXiv:1308.3197</a> <span> [<a href="https://arxiv.org/pdf/1308.3197">pdf</a>, <a href="https://arxiv.org/ps/1308.3197">ps</a>, <a href="https://arxiv.org/format/1308.3197">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/0004-637X/788/1/70">10.1088/0004-637X/788/1/70 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> "Self-absorbed" GeV light-curves of Gamma-Ray Burst afterglows </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Vestrand%2C+W+T">W. T. Vestrand</a>, <a href="/search/astro-ph?searchtype=author&query=Wozniak%2C+P">P. Wozniak</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1308.3197v2-abstract-short" style="display: inline;"> We investigate the effect that the absorption of high-energy (above 100 MeV) photons produced in GRB afterglow shocks has on the light-curves and spectra of Fermi-LAT afterglows. Afterglows produced by the interaction of a relativistic outflow with a wind-like medium peak when the blast-wave deceleration sets in, and the afterglow spectrum could be hardening before that peak, as the optical thickn… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1308.3197v2-abstract-full').style.display = 'inline'; document.getElementById('1308.3197v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1308.3197v2-abstract-full" style="display: none;"> We investigate the effect that the absorption of high-energy (above 100 MeV) photons produced in GRB afterglow shocks has on the light-curves and spectra of Fermi-LAT afterglows. Afterglows produced by the interaction of a relativistic outflow with a wind-like medium peak when the blast-wave deceleration sets in, and the afterglow spectrum could be hardening before that peak, as the optical thickness to pair-formation is decreasing. In contrast, in afterglows produced in the interaction with a homogeneous medium, the optical thickness to pair-formation should increase and yield a light-curve peak when it reaches unity, followed by a fast light-curve decay, accompanied by a spectral softening. If energy is injected in the blast-wave, then the accelerated increase of the optical thickness yields a convex afterglow light-curve. Other features, such as a double-peak light-curve or a broad hump, can arise from the evolution of the optical thickness to photon-photon absorption. Fast decays and convex light-curves are seen in a few LAT afterglows, but the expected spectral softening is rarely seen in (and difficult to measure with) LAT observations. Furthermore, for the effects of photon-photon attenuation to shape the high-energy afterglow light-curve without attenuating it too much, the ejecta initial Lorentz factor must be in a relatively narrow range (50-200), which reduces the chance of observing those effects. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1308.3197v2-abstract-full').style.display = 'none'; document.getElementById('1308.3197v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 22 April, 2014; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 14 August, 2013; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2013. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">8 pages, to appear in the ApJ</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1305.0809">arXiv:1305.0809</a> <span> [<a href="https://arxiv.org/pdf/1305.0809">pdf</a>, <a href="https://arxiv.org/ps/1305.0809">ps</a>, <a href="https://arxiv.org/format/1305.0809">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1093/mnras/stt769">10.1093/mnras/stt769 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Peaks of optical and X-ray afterglow light-curves </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Vestrand%2C+W+T">W. T. Vestrand</a>, <a href="/search/astro-ph?searchtype=author&query=Wozniak%2C+P">P. Wozniak</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1305.0809v1-abstract-short" style="display: inline;"> The peaks of 30 optical afterglows and 14 X-ray light-curves display a good anticorrelation of the peak flux with the peak epoch: F_p ~ t_p^{-2.0} in the optical, F_p ~ t_p^{-1.6} in the X-ray, the distributions of the peak epochs being consistent with each other. We investigate the ability of two forward-shock models for afterglow light-curve peaks -- an observer location outside the initial jet… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1305.0809v1-abstract-full').style.display = 'inline'; document.getElementById('1305.0809v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1305.0809v1-abstract-full" style="display: none;"> The peaks of 30 optical afterglows and 14 X-ray light-curves display a good anticorrelation of the peak flux with the peak epoch: F_p ~ t_p^{-2.0} in the optical, F_p ~ t_p^{-1.6} in the X-ray, the distributions of the peak epochs being consistent with each other. We investigate the ability of two forward-shock models for afterglow light-curve peaks -- an observer location outside the initial jet aperture and the onset of the forward-shock deceleration -- to account for those peak correlations. For both models, the slope of the F_p - t_p relation depends only on the slope of the afterglow spectrum. We find that only a conical jet seen off-aperture and interacting with a wind-like medium can account for both the X-ray peak relation, given the average X-ray spectral slope beta_x = 1.0, and for the larger slope of the optical peak relation. However, any conclusion about the origin of the peak flux - peak epoch correlation is, at best, tentative, because the current sample of X-ray peaks is too small to allow a reliable measurement of the F_p - t_p relation slope and because more than one mechanism and/or one afterglow parameter may be driving that correlation. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1305.0809v1-abstract-full').style.display = 'none'; document.getElementById('1305.0809v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 3 May, 2013; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2013. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">13 pages, to appear in MNRAS</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1212.1486">arXiv:1212.1486</a> <span> [<a href="https://arxiv.org/pdf/1212.1486">pdf</a>, <a href="https://arxiv.org/ps/1212.1486">ps</a>, <a href="https://arxiv.org/format/1212.1486">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2012.21595.x">10.1111/j.1365-2966.2012.21595.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> The possible ubiquity of energy injection in Gamma-Ray Burst afterglows </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Vestrand%2C+W+T">W. T. Vestrand</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1212.1486v1-abstract-short" style="display: inline;"> Since its launch in 2004, the Swift satellite has monitored the X-ray afterglows of several hundred Gamma-Ray Bursts, and revealed that their X-ray light-curves are more complex than previously thought, exhibiting up to three power-law segments. Energy injection into the relativistic blast-wave energizing the burst ambient medium has been proposed most often to be the reason for the X-ray afterglo… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1212.1486v1-abstract-full').style.display = 'inline'; document.getElementById('1212.1486v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1212.1486v1-abstract-full" style="display: none;"> Since its launch in 2004, the Swift satellite has monitored the X-ray afterglows of several hundred Gamma-Ray Bursts, and revealed that their X-ray light-curves are more complex than previously thought, exhibiting up to three power-law segments. Energy injection into the relativistic blast-wave energizing the burst ambient medium has been proposed most often to be the reason for the X-ray afterglow complexity. We examine 117 light-curve breaks of 98 Swift X-ray afterglows, selected for their high-quality monitoring and well-constrained flux decay rates. Thirty percent of afterglows have a break that can be an adiabatic jet-break, in the sense that there is one variant of the forward-shock emission from a collimated outflow model that can account for both the pre- and post-break flux power-law decay indices, given the measured X-ray spectral slope. If allowance is made for a steady energy injection into the forward-shock, then another 56 percent of X-ray afterglows have a light-curve break that can be explained with a jet-break. The remaining 12 percent that are not jet-breaks, as well as the existence of two breaks in 19 afterglows (out of which only one can be a jet-break), suggest that some X-ray breaks arise from a sudden change in the rate at which energy is added to the blast-wave, and it may well be that a larger fraction of X-ray light-curve breaks are generated by that mechanism. To test the above two mechanisms for afterglow light-curve breaks, we derive comprehensive analytical results for the dynamics of outflows undergoing energy injection and for their light-curves, including closure relations for inverse-Compton afterglows and for the emission from spreading jets interacting with an wind-like ambient medium. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1212.1486v1-abstract-full').style.display = 'none'; document.getElementById('1212.1486v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 6 December, 2012; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> December 2012. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">14 pages</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> MNRAS 425, 1669 (2012) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1209.4658">arXiv:1209.4658</a> <span> [<a href="https://arxiv.org/pdf/1209.4658">pdf</a>, <a href="https://arxiv.org/ps/1209.4658">ps</a>, <a href="https://arxiv.org/format/1209.4658">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1051/0004-6361/201219583">10.1051/0004-6361/201219583 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> GRB 091029: At the limit of the fireball scenario </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Filgas%2C+R">R. Filgas</a>, <a href="/search/astro-ph?searchtype=author&query=Greiner%2C+J">J. Greiner</a>, <a href="/search/astro-ph?searchtype=author&query=Schady%2C+P">P. Schady</a>, <a href="/search/astro-ph?searchtype=author&query=Postigo%2C+A+d+U">A. de Ugarte Postigo</a>, <a href="/search/astro-ph?searchtype=author&query=Oates%2C+S+R">S. R. Oates</a>, <a href="/search/astro-ph?searchtype=author&query=Nardini%2C+M">M. Nardini</a>, <a href="/search/astro-ph?searchtype=author&query=Kruehler%2C+T">T. Kruehler</a>, <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Kann%2C+D+A">D. A. Kann</a>, <a href="/search/astro-ph?searchtype=author&query=Klose%2C+S">S. Klose</a>, <a href="/search/astro-ph?searchtype=author&query=Afonso%2C+P+M+J">P. M. J. Afonso</a>, <a href="/search/astro-ph?searchtype=author&query=Allen%2C+W+H">W. H. Allen</a>, <a href="/search/astro-ph?searchtype=author&query=Castro-Tirado%2C+A+J">A. J. Castro-Tirado</a>, <a href="/search/astro-ph?searchtype=author&query=Christie%2C+G+W">G. W. Christie</a>, <a href="/search/astro-ph?searchtype=author&query=Dong%2C+S">S. Dong</a>, <a href="/search/astro-ph?searchtype=author&query=Elliott%2C+J">J. Elliott</a>, <a href="/search/astro-ph?searchtype=author&query=Natusch%2C+T">T. Natusch</a>, <a href="/search/astro-ph?searchtype=author&query=Guelbenzu%2C+A+N">A. Nicuesa Guelbenzu</a>, <a href="/search/astro-ph?searchtype=author&query=E.%2C+F+O">F. Olivares E.</a>, <a href="/search/astro-ph?searchtype=author&query=Rau%2C+A">A. Rau</a>, <a href="/search/astro-ph?searchtype=author&query=Rossi%2C+A">A. Rossi</a>, <a href="/search/astro-ph?searchtype=author&query=Sudilovsky%2C+V">V. Sudilovsky</a>, <a href="/search/astro-ph?searchtype=author&query=Yock%2C+P+C+M">P. C. M. Yock</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1209.4658v1-abstract-short" style="display: inline;"> Using high-quality, broad-band afterglow data for GRB 091029, we test the validity of the forward-shock model for gamma-ray burst afterglows. We used multi-wavelength (NIR to X-ray) follow-up observations obtained with the GROND, BOOTES-3/YA and Stardome optical ground-based telescopes, and the UVOT and the XRT onboard the Swift satellite. To explain the almost totally decoupled light curves in th… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1209.4658v1-abstract-full').style.display = 'inline'; document.getElementById('1209.4658v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1209.4658v1-abstract-full" style="display: none;"> Using high-quality, broad-band afterglow data for GRB 091029, we test the validity of the forward-shock model for gamma-ray burst afterglows. We used multi-wavelength (NIR to X-ray) follow-up observations obtained with the GROND, BOOTES-3/YA and Stardome optical ground-based telescopes, and the UVOT and the XRT onboard the Swift satellite. To explain the almost totally decoupled light curves in the X-ray and optical/NIR domains, a two-component outflow is proposed. Several models are tested, including continuous energy injection, components with different electron energy indices and components in two different stages of spectral evolution. Only the last model can explain both the decoupled light curves with asynchronous peaks and the peculiar SED evolution. However, this model has so many unknown free parameters that we are unable to reliably confirm or disprove its validity, making the afterglow of GRB 091029 difficult to explain in the framework of the simplest fireball model. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1209.4658v1-abstract-full').style.display = 'none'; document.getElementById('1209.4658v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 20 September, 2012; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2012. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Accepted to A&A</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1201.4181">arXiv:1201.4181</a> <span> [<a href="https://arxiv.org/pdf/1201.4181">pdf</a>, <a href="https://arxiv.org/ps/1201.4181">ps</a>, <a href="https://arxiv.org/format/1201.4181">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/0004-637X/761/1/50">10.1088/0004-637X/761/1/50 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Broadband study of GRB 091127: a sub-energetic burst at higher redshift? </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Troja%2C+E">E. Troja</a>, <a href="/search/astro-ph?searchtype=author&query=Sakamoto%2C+T">T. Sakamoto</a>, <a href="/search/astro-ph?searchtype=author&query=Guidorzi%2C+C">C. Guidorzi</a>, <a href="/search/astro-ph?searchtype=author&query=Norris%2C+J+P">J. P. Norris</a>, <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Kobayashi%2C+S">S. Kobayashi</a>, <a href="/search/astro-ph?searchtype=author&query=Omodei%2C+N">N. Omodei</a>, <a href="/search/astro-ph?searchtype=author&query=Brown%2C+J+C">J. C. Brown</a>, <a href="/search/astro-ph?searchtype=author&query=Burrows%2C+D+N">D. N. Burrows</a>, <a href="/search/astro-ph?searchtype=author&query=Evans%2C+P+A">P. A. Evans</a>, <a href="/search/astro-ph?searchtype=author&query=Gehrels%2C+N">N. Gehrels</a>, <a href="/search/astro-ph?searchtype=author&query=Marshall%2C+F+E">F. E. Marshall</a>, <a href="/search/astro-ph?searchtype=author&query=Mawson%2C+N">N. Mawson</a>, <a href="/search/astro-ph?searchtype=author&query=Melandri%2C+A">A. Melandri</a>, <a href="/search/astro-ph?searchtype=author&query=Mundell%2C+C+G">C. G. Mundell</a>, <a href="/search/astro-ph?searchtype=author&query=Oates%2C+S+R">S. R. Oates</a>, <a href="/search/astro-ph?searchtype=author&query=Pal%27shin%2C+V">V. Pal'shin</a>, <a href="/search/astro-ph?searchtype=author&query=Preece%2C+R+D">R. D. Preece</a>, <a href="/search/astro-ph?searchtype=author&query=Racusin%2C+J+L">J. L. Racusin</a>, <a href="/search/astro-ph?searchtype=author&query=Steele%2C+I+A">I. A. Steele</a>, <a href="/search/astro-ph?searchtype=author&query=Tanvir%2C+N+R">N. R. Tanvir</a>, <a href="/search/astro-ph?searchtype=author&query=Vasileiou%2C+V">V. Vasileiou</a>, <a href="/search/astro-ph?searchtype=author&query=Wilson-Hodge%2C+C">C. Wilson-Hodge</a>, <a href="/search/astro-ph?searchtype=author&query=Yamaoka%2C+K">K. Yamaoka</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1201.4181v1-abstract-short" style="display: inline;"> GRB 091127 is a bright gamma-ray burst (GRB) detected by Swift at a redshift z=0.49 and associated with SN 2009nz. We present the broadband analysis of the GRB prompt and afterglow emission and study its high-energy properties in the context of the GRB/SN association. While the high luminosity of the prompt emission and standard afterglow behavior are typical of cosmological long GRBs, its low ene… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1201.4181v1-abstract-full').style.display = 'inline'; document.getElementById('1201.4181v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1201.4181v1-abstract-full" style="display: none;"> GRB 091127 is a bright gamma-ray burst (GRB) detected by Swift at a redshift z=0.49 and associated with SN 2009nz. We present the broadband analysis of the GRB prompt and afterglow emission and study its high-energy properties in the context of the GRB/SN association. While the high luminosity of the prompt emission and standard afterglow behavior are typical of cosmological long GRBs, its low energy release, soft spectrum and unusual spectral lag connect this GRB to the class of sub-energetic bursts. We discuss the suppression of high-energy emission in this burst, and investigate whether this behavior could be connected with the sub-energetic nature of the explosion. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1201.4181v1-abstract-full').style.display = 'none'; document.getElementById('1201.4181v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 19 January, 2012; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> January 2012. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">12 pages, 7 figures, submitted to ApJ</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1009.3947">arXiv:1009.3947</a> <span> [<a href="https://arxiv.org/pdf/1009.3947">pdf</a>, <a href="https://arxiv.org/ps/1009.3947">ps</a>, <a href="https://arxiv.org/format/1009.3947">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2011.18653.x">10.1111/j.1365-2966.2011.18653.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Optical afterglows of Gamma-Ray Bursts: peaks, plateaus, and possibilities </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Vestrand%2C+W+T">W. T. Vestrand</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1009.3947v2-abstract-short" style="display: inline;"> The optical light-curves of GRB afterglows display either peaks or plateaus. We identify 16 afterglows of the former type, 17 of the latter, and 4 with broad peaks, that could be of either type. The optical energy release of these two classes is similar and is correlated with the GRB output, the correlation being stronger for peaky afterglows, which suggests that the burst and afterglow emission… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1009.3947v2-abstract-full').style.display = 'inline'; document.getElementById('1009.3947v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1009.3947v2-abstract-full" style="display: none;"> The optical light-curves of GRB afterglows display either peaks or plateaus. We identify 16 afterglows of the former type, 17 of the latter, and 4 with broad peaks, that could be of either type. The optical energy release of these two classes is similar and is correlated with the GRB output, the correlation being stronger for peaky afterglows, which suggests that the burst and afterglow emissions of peaky afterglows are from the same relativistic ejecta and that the optical emission of afterglows with plateaus arises more often from ejecta that did not produce the burst emission. Consequently, we propose that peaky optical afterglows are from impulsive ejecta releases and that plateau optical afterglows originate from long-lived engines, the break in the optical light-curve (peak or plateau end) marking the onset of the entire outflow deceleration. In the peak luminosity--peak time plane, the distribution of peaky afterglows displays an edge with L_p \propto t_p^{-3}, which we attribute to variations (among afterglows) in the ambient medium density. The fluxes and epochs of optical plateau breaks follow a L_b \propto t_b^{-1} anticorrelation. Sixty percent of 25 afterglows that were well-monitored in the optical and X-rays show light-curves with comparable power-law decays indices and achromatic breaks. The other 40 percent display three types of decoupled behaviours: i) chromatic optical light-curve breaks (perhaps due to the peak of the synchrotron spectrum crossing the optical), ii) X-ray flux decays faster than in the optical (suggesting that the X-ray emission is from local inverse-Compton scattering), and iii) chromatic X-ray light-curve breaks (indicating that the X-ray emission is from external up-scattering). <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1009.3947v2-abstract-full').style.display = 'none'; document.getElementById('1009.3947v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 7 March, 2011; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 20 September, 2010; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2010. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">11 pages, table with afterglows added, to appear in MNRAS</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1007.0383">arXiv:1007.0383</a> <span> [<a href="https://arxiv.org/pdf/1007.0383">pdf</a>, <a href="https://arxiv.org/ps/1007.0383">ps</a>, <a href="https://arxiv.org/format/1007.0383">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1051/0004-6361/201015324">10.1051/0004-6361/201015324 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> The Swift/Fermi GRB 080928 from 1 eV to 150 keV </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Rossi%2C+A">A. Rossi</a>, <a href="/search/astro-ph?searchtype=author&query=Schulze%2C+S">S. Schulze</a>, <a href="/search/astro-ph?searchtype=author&query=Klose%2C+S">S. Klose</a>, <a href="/search/astro-ph?searchtype=author&query=Kann%2C+D+A">D. A. Kann</a>, <a href="/search/astro-ph?searchtype=author&query=Rau%2C+A">A. Rau</a>, <a href="/search/astro-ph?searchtype=author&query=Krimm%2C+H+A">H. A. Krimm</a>, <a href="/search/astro-ph?searchtype=author&query=J%C3%B3hannesson%2C+G">G. J贸hannesson</a>, <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Yuan%2C+F">F. Yuan</a>, <a href="/search/astro-ph?searchtype=author&query=Ferrero%2C+P">P. Ferrero</a>, <a href="/search/astro-ph?searchtype=author&query=Kr%C3%BChler%2C+T">T. Kr眉hler</a>, <a href="/search/astro-ph?searchtype=author&query=Greiner%2C+J">J. Greiner</a>, <a href="/search/astro-ph?searchtype=author&query=Schady%2C+P">P. Schady</a>, <a href="/search/astro-ph?searchtype=author&query=Pandey%2C+S+B">S. B. Pandey</a>, <a href="/search/astro-ph?searchtype=author&query=Amati%2C+L">L. Amati</a>, <a href="/search/astro-ph?searchtype=author&query=Afonso%2C+P+M+J">P. M. J. Afonso</a>, <a href="/search/astro-ph?searchtype=author&query=Akerlof%2C+C+W">C. W. Akerlof</a>, <a href="/search/astro-ph?searchtype=author&query=Arnold%2C+L">L. Arnold</a>, <a href="/search/astro-ph?searchtype=author&query=Clemens%2C+C">C. Clemens</a>, <a href="/search/astro-ph?searchtype=author&query=Filgas%2C+R">R. Filgas</a>, <a href="/search/astro-ph?searchtype=author&query=Hartmann%2C+D+H">D. H. Hartmann</a>, <a href="/search/astro-ph?searchtype=author&query=Yolda%C5%9F%2C+A+K">A. K眉pc眉 Yolda艧</a>, <a href="/search/astro-ph?searchtype=author&query=McBreen%2C+S">S. McBreen</a>, <a href="/search/astro-ph?searchtype=author&query=McKay%2C+T+A">T. A. McKay</a>, <a href="/search/astro-ph?searchtype=author&query=Guelbenzu%2C+A+N">A. Nicuesa Guelbenzu</a> , et al. (6 additional authors not shown) </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1007.0383v4-abstract-short" style="display: inline;"> We present the results of a comprehensive study of the gamma-ray burst 080928 and of its afterglow. GRB 080928 was a long burst detected by Swift/BAT and Fermi/GBM. It is one of the exceptional cases where optical emission had already been detected when the GRB itself was still radiating in the gamma-ray band. For nearly 100 seconds simultaneous optical, X-ray and gamma-ray data provide a coverage… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1007.0383v4-abstract-full').style.display = 'inline'; document.getElementById('1007.0383v4-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1007.0383v4-abstract-full" style="display: none;"> We present the results of a comprehensive study of the gamma-ray burst 080928 and of its afterglow. GRB 080928 was a long burst detected by Swift/BAT and Fermi/GBM. It is one of the exceptional cases where optical emission had already been detected when the GRB itself was still radiating in the gamma-ray band. For nearly 100 seconds simultaneous optical, X-ray and gamma-ray data provide a coverage of the spectral energy distribution of the transient source from about 1 eV to 150 keV. In particular, we show that the SED during the main prompt emission phase agrees with synchrotron radiation. We constructed the optical/near-infrared light curve and the spectral energy distribution based on Swift/UVOT, ROTSE-IIIa (Australia), and GROND (La Silla) data and compared it to the X-ray light curve retrieved from the Swift/XRT repository. We show that its bumpy shape can be modeled by multiple energy-injections into the forward shock.Furthermore, we investigate whether the temporal and spectral evolution of the tail emission of the first strong flare seen in the early X-ray light curve can be explained by large-angle emission (LAE). We find that a nonstandard LAE model is required to explain the observations. Finally, we report on the results of our search for the GRB host galaxy, for which only a deep upper limit can be provided. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1007.0383v4-abstract-full').style.display = 'none'; document.getElementById('1007.0383v4-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 25 March, 2011; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 2 July, 2010; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> July 2010. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">A&A, in press (including revisions according to the language editor), 14 pages, 11 figures, 7 tables; Online Appendix: 4 pages, 1 figure, 4 tables; v4: final journal version to be published soon</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1005.1051">arXiv:1005.1051</a> <span> [<a href="https://arxiv.org/pdf/1005.1051">pdf</a>, <a href="https://arxiv.org/ps/1005.1051">ps</a>, <a href="https://arxiv.org/format/1005.1051">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2011.18469.x">10.1111/j.1365-2966.2011.18469.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> GRB 090510: a short burst from a massive star ? </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1005.1051v2-abstract-short" style="display: inline;"> GRB afterglow 090510 is (so far) the best-monitored afterglow in the optical, X-ray, and above 100 MeV, measurements covering 2-3 decades in time at each frequency. Owing to its power-law temporal decay and power-law spectrum, it seems very likely that the highest energy emission is from the forward-shock energizing the ambient medium (the standard blast-wave model for GRB afterglows), the GeV flu… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1005.1051v2-abstract-full').style.display = 'inline'; document.getElementById('1005.1051v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1005.1051v2-abstract-full" style="display: none;"> GRB afterglow 090510 is (so far) the best-monitored afterglow in the optical, X-ray, and above 100 MeV, measurements covering 2-3 decades in time at each frequency. Owing to its power-law temporal decay and power-law spectrum, it seems very likely that the highest energy emission is from the forward-shock energizing the ambient medium (the standard blast-wave model for GRB afterglows), the GeV flux and its decay rate being consistent with that model's expectations. However, the synchrotron emission from a collimated outflow (the standard jet model) has difficulties in accounting for the lower-energy afterglow emission, where a simultaneous break occurs at 2 ks in the optical and X-ray light-curves, but with the optical flux decay (before and after the break) being much slower than in the X-rays (at same time). The measured X-ray and GeV fluxes are incompatible with the higher-energy afterglow emission being from same spectral component as the lower-energy afterglow emission, which suggests a synchrotron self-Compton model for this afterglow. Cessation of energy injection in the blast-wave and an ambient medium with a wind-like n ~ r^{-2} density can explain all features of the optical and X-ray light-curves of GRB afterglow 090510. Such an ambient medium radial structure is incompatible with this short-GRB originating from the merger of two compact stars. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1005.1051v2-abstract-full').style.display = 'none'; document.getElementById('1005.1051v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 2 February, 2011; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 6 May, 2010; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2010. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">12 pages, to appear in MNRAS</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/0812.1038">arXiv:0812.1038</a> <span> [<a href="https://arxiv.org/pdf/0812.1038">pdf</a>, <a href="https://arxiv.org/ps/0812.1038">ps</a>, <a href="https://arxiv.org/format/0812.1038">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1063/1.3155864">10.1063/1.3155864 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Gamma-Ray Burst afterglows: theory and observations </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="0812.1038v1-abstract-short" style="display: inline;"> I discuss some theoretical expectations for the synchrotron emission from a relativistic blast-wave interacting with the ambient medium, as a model for GRB afterglows, and compare them with observations. An afterglow flux evolving as a power-law in time, a bright optical flash during/after the burst, and a light-curve break due to a tight ejecta collimation are the major predictions that were co… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0812.1038v1-abstract-full').style.display = 'inline'; document.getElementById('0812.1038v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="0812.1038v1-abstract-full" style="display: none;"> I discuss some theoretical expectations for the synchrotron emission from a relativistic blast-wave interacting with the ambient medium, as a model for GRB afterglows, and compare them with observations. An afterglow flux evolving as a power-law in time, a bright optical flash during/after the burst, and a light-curve break due to a tight ejecta collimation are the major predictions that were confirmed observationally, but it should be recognized that light-curve decay indices are not correlated with the spectral slopes (as would be expected), optical flashes are quite rare, and jet-breaks harder to find in Swift X-ray afterglows. The slowing of the early optical flux decay rate is accompanied by a spectral evolution, indicating that the emission from ejecta (energized by the reverse shock) is dominant in the optical over that from the forward shock (which energizes the ambient medium) only up to 1 ks. However, a long-lived reverse shock is required to account for the slow radio flux decays observed in many afterglows after ~10 day. X-ray light-curve plateaus could be due to variations in the average energy-per-solid-angle of the blast-wave, confirming to two other anticipated features of GRB outflows: energy injection and angular structure. The latter is also the more likely origin of the fast-rises seen in some optical light-curves. To account for the existence of both chromatic and achromatic afterglow light-curve breaks, the overall picture must be even more complex and include a new mechanism that dominates occasionally the emission from the blast-wave: either late internal shocks or scattering (bulk and/or inverse-Compton) of the blast-wave emission by an outflow interior to it. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0812.1038v1-abstract-full').style.display = 'none'; document.getElementById('0812.1038v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 4 December, 2008; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> December 2008. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">16 pages, article based on review talk given at Fermi/Swift meeting (Oct 08), to be published in AIP conference proceedings</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> AIP Conf.Proc.1133:127-138,2009 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/0811.2163">arXiv:0811.2163</a> <span> [<a href="https://arxiv.org/pdf/0811.2163">pdf</a>, <a href="https://arxiv.org/ps/0811.2163">ps</a>, <a href="https://arxiv.org/format/0811.2163">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2008.14240.x">10.1111/j.1365-2966.2008.14240.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> An external-shock origin of the E_p-E_gamma relation for Gamma-Ray Bursts </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="0811.2163v1-abstract-short" style="display: inline;"> We investigate the possibility that the E_p propto E_gamma^{1/2} relation between the peak energy E_p of the nuF_nu spectrum and energy output E_gamma for long-duration GRBs arises from the external shock produced by the interaction of a relativistic outflow with the ambient medium. To that aim, we take into account the dependence of all parameters which determine E_p and E_gamma on the radial d… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0811.2163v1-abstract-full').style.display = 'inline'; document.getElementById('0811.2163v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="0811.2163v1-abstract-full" style="display: none;"> We investigate the possibility that the E_p propto E_gamma^{1/2} relation between the peak energy E_p of the nuF_nu spectrum and energy output E_gamma for long-duration GRBs arises from the external shock produced by the interaction of a relativistic outflow with the ambient medium. To that aim, we take into account the dependence of all parameters which determine E_p and E_gamma on the radial distribution of the ambient medium density and find that the E_p-E_gamma relation can be explained if the medium around GRBs has a universal radial stratification. For various combinations of GRB radiative process (synchrotron or inverse-Compton) and dissipation mechanism (reverse or forward shock), we find that the circumburst medium must have a particle density with a radial distribution different than the R^{-2} expected for constant mass-loss rate and terminal speed. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0811.2163v1-abstract-full').style.display = 'none'; document.getElementById('0811.2163v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 13 November, 2008; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> November 2008. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">6 pages, to appear in MNRAS</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Mon.Not.Roy.Astron.Soc.393:1010-1015,2009 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/0811.1235">arXiv:0811.1235</a> <span> [<a href="https://arxiv.org/pdf/0811.1235">pdf</a>, <a href="https://arxiv.org/ps/0811.1235">ps</a>, <a href="https://arxiv.org/format/0811.1235">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> </div> <p class="title is-5 mathjax"> Prompt GeV emission in the synchrotron self-Compton model for Gamma-Ray Bursts </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="0811.1235v1-abstract-short" style="display: inline;"> The detection in 10 bursts of an optical counterpart emission (i.e. during the prompt GRB phase) that is 10-10000 brighter than the extrapolation of the burst spectrum to optical frequencies suggests a synchrotron self-Compton origin for the GRB emission, synchrotron producing the optical counterpart emission. In this model, the second upscattering of the burst photons yields a prompt GeV-TeV em… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0811.1235v1-abstract-full').style.display = 'inline'; document.getElementById('0811.1235v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="0811.1235v1-abstract-full" style="display: none;"> The detection in 10 bursts of an optical counterpart emission (i.e. during the prompt GRB phase) that is 10-10000 brighter than the extrapolation of the burst spectrum to optical frequencies suggests a synchrotron self-Compton origin for the GRB emission, synchrotron producing the optical counterpart emission. In this model, the second upscattering of the burst photons yields a prompt GeV-TeV emission, whose brightness depends strongly on an unknown quantity, the peak energy of the primary synchrotron spectrum. Measurements of the optical, gamma-ray, and GeV prompt fluxes can be used to test the synchrotron self-Compton model for GRBs and to determine directly the total radiative output of GRBs. For a set of 29 GRBs with optical counterpart detections, we find that the expected GeV photon flux should correlate with the fluence of the sub-MeV emission and should anticorrelate with the brightness of the optical counterpart, the strength of these correlations decreasing for an increasing width of the synchrotron peak energy distribution. The detection of a GeV prompt emission consistent with the extrapolation of the burst spectrum to higher energies would rule out the synchrotron self-Compton model if the sub-MeV burst emission were very bright and the (intrinsic) optical counterpart were very dim. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0811.1235v1-abstract-full').style.display = 'none'; document.getElementById('0811.1235v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 7 November, 2008; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> November 2008. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">9 pages, submitted to MNRAS</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/0810.2481">arXiv:0810.2481</a> <span> [<a href="https://arxiv.org/pdf/0810.2481">pdf</a>, <a href="https://arxiv.org/ps/0810.2481">ps</a>, <a href="https://arxiv.org/format/0810.2481">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/0004-637X/691/1/495">10.1088/0004-637X/691/1/495 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Gamma-Ray Burst at the extreme: "the naked-eye burst" GRB 080319B </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Wozniak%2C+P+R">P. R. Wozniak</a>, <a href="/search/astro-ph?searchtype=author&query=Vestrand%2C+W+T">W. T. Vestrand</a>, <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A+D">A. D. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Wren%2C+J+A">J. A. Wren</a>, <a href="/search/astro-ph?searchtype=author&query=Davis%2C+H+R">H. R. Davis</a>, <a href="/search/astro-ph?searchtype=author&query=White%2C+R+R">R. R. White</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="0810.2481v1-abstract-short" style="display: inline;"> On 19 March 2008, the northern sky was the stage of a spectacular optical transient that for a few seconds remained visible to the naked eye. The transient was associated with GRB 080319B, a gamma-ray burst at a luminosity distance of about 6 Gpc (standard cosmology), making it the most luminous optical object ever recorded by human kind. We present comprehensive sky monitoring and multi-color o… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0810.2481v1-abstract-full').style.display = 'inline'; document.getElementById('0810.2481v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="0810.2481v1-abstract-full" style="display: none;"> On 19 March 2008, the northern sky was the stage of a spectacular optical transient that for a few seconds remained visible to the naked eye. The transient was associated with GRB 080319B, a gamma-ray burst at a luminosity distance of about 6 Gpc (standard cosmology), making it the most luminous optical object ever recorded by human kind. We present comprehensive sky monitoring and multi-color optical follow-up observations of GRB 080319B collected by the RAPTOR telescope network covering the development of the explosion and the afterglow before, during, and after the burst. The extremely bright prompt optical emission revealed features that are normally not detectable. The optical and gamma-ray variability during the explosion are correlated, but the optical flux is much greater than can be reconciled with single emission mechanism and a flat gamma-ray spectrum. This extreme optical behavior is best understood as synchrotron self-Compton model (SSC). After a gradual onset of the gamma-ray emission, there is an abrupt rise of the prompt optical flux suggesting that variable self-absorption dominates the early optical light curve. Our simultaneous multi-color optical light curves following the flash show spectral evolution consistent with a rapidly decaying red component due to large angle emission and the emergence of a blue forward shock component from interaction with the surrounding environment. While providing little support for the reverse shock that dominates the early afterglow, these observations strengthen the case for the universal role of the SSC mechanism in generating gamma-ray bursts. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0810.2481v1-abstract-full').style.display = 'none'; document.getElementById('0810.2481v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 14 October, 2008; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> October 2008. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">accepted for publication in ApJ</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Astrophys.J.691:495-502,2009 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/0805.0144">arXiv:0805.0144</a> <span> [<a href="https://arxiv.org/pdf/0805.0144">pdf</a>, <a href="https://arxiv.org/ps/0805.0144">ps</a>, <a href="https://arxiv.org/format/0805.0144">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1745-3933.2008.00546.x">10.1111/j.1745-3933.2008.00546.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> What did we learn from gamma-ray burst 080319B ? </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Kumar%2C+P">P. Kumar</a>, <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="0805.0144v2-abstract-short" style="display: inline;"> The optical and gamma-ray observations of GRB 080319B allow us to determine a fairly complete physical picture for this remarkable burst. The data indicate that the prompt optical and gamma-ray photons were produced at the same location but by different radiation processes: synchrotron and synchrotron self-Compton, respectively. The burst emission was produced at a distance of 10^{16.5} cm from… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0805.0144v2-abstract-full').style.display = 'inline'; document.getElementById('0805.0144v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="0805.0144v2-abstract-full" style="display: none;"> The optical and gamma-ray observations of GRB 080319B allow us to determine a fairly complete physical picture for this remarkable burst. The data indicate that the prompt optical and gamma-ray photons were produced at the same location but by different radiation processes: synchrotron and synchrotron self-Compton, respectively. The burst emission was produced at a distance of 10^{16.5} cm from the center of explosion by an ultra-relativistic source moving at Lorentz factor of ~500. A straightforward inference is that about 10 times more energy must have been radiated at tens of GeV than that released at ~1 MeV. Assuming that the GRB outflow was baryonic and that the gamma-ray source was shock-heated plasma, the collimation-corrected kinetic energy of the jet powering GRB 080319B was larger than 10^{52.3} erg. The decay of the early afterglow optical emission (up to 1 ks) is too fast to be attributed to the reverse shock crossing the GRB ejecta but is consistent with the expectations for the "large-angle emission" released during the burst. The pure power-law decay of the optical afterglow flux from 1 ks to 10 day is most naturally identified with the (synchrotron) emission from the shock propagating into a wind-like medium. However, the X-ray afterglow requires a departure from the standard blast-wave model. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0805.0144v2-abstract-full').style.display = 'none'; document.getElementById('0805.0144v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 12 August, 2008; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 1 May, 2008; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2008. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">5 pages, to appear in MNRAS Letters, potential difficulties of the SSC model discussed in S2.2</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Mon.Not.Roy.Astron.Soc. 391:L19-23,2008 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/0803.1872">arXiv:0803.1872</a> <span> [<a href="https://arxiv.org/pdf/0803.1872">pdf</a>, <a href="https://arxiv.org/ps/0803.1872">ps</a>, <a href="https://arxiv.org/format/0803.1872">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2008.13231.x">10.1111/j.1365-2966.2008.13231.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Taxonomy of GRB optical light-curves: identification of a salient class of early afterglows </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Vestrand%2C+W+T">W. T. Vestrand</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="0803.1872v1-abstract-short" style="display: inline;"> The temporal behaviour of the early optical emission from Gamma-Ray Burst afterglows can be divided in four classes: fast-rising with an early peak, slow-rising with a late peak, flat plateaus, and rapid decays since first measurement. The fast-rising optical afterglows display correlations among peak flux, peak epoch, and post-peak power-law decay index that can be explained with a structured o… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0803.1872v1-abstract-full').style.display = 'inline'; document.getElementById('0803.1872v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="0803.1872v1-abstract-full" style="display: none;"> The temporal behaviour of the early optical emission from Gamma-Ray Burst afterglows can be divided in four classes: fast-rising with an early peak, slow-rising with a late peak, flat plateaus, and rapid decays since first measurement. The fast-rising optical afterglows display correlations among peak flux, peak epoch, and post-peak power-law decay index that can be explained with a structured outflow seen off-axis, but the shock origin (reverse or forward) of the optical emission cannot be determined. The afterglows with plateaus and slow-rises may be accommodated by the same model, if observer location offsets are larger than for the fast-rising afterglows, or could be due to a long-lived injection of energy and/or ejecta in the blast-wave. If better calibrated with more afterglows, the peak flux-peak epoch relation exhibited by the fast and slow-rising optical light-curves could provide a way to use this type of afterglows as standard candles. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0803.1872v1-abstract-full').style.display = 'none'; document.getElementById('0803.1872v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 12 March, 2008; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2008. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">8 pages, submitted to MNRAS</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Mon.Not.Roy.Astron.Soc. 387 (2008) 497-504 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/0802.1235">arXiv:0802.1235</a> <span> [<a href="https://arxiv.org/pdf/0802.1235">pdf</a>, <a href="https://arxiv.org/ps/0802.1235">ps</a>, <a href="https://arxiv.org/format/0802.1235">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1063/1.2943502">10.1063/1.2943502 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Direct and bulk-scattered forward-shock emissions: sources of X-ray afterglow diversity </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="0802.1235v1-abstract-short" style="display: inline;"> I describe the modifications to the standard forward-shock model required to account for the X-ray light-curve features discovered by Swift in the early afterglow emission and propose that a delayed, pair-enriched, and highly relativistic outflow, which bulk-scatters the forward-shock synchrotron emission, yields sometimes a brighter X-ray emission, producing short-lived X-ray flares, X-ray ligh… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0802.1235v1-abstract-full').style.display = 'inline'; document.getElementById('0802.1235v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="0802.1235v1-abstract-full" style="display: none;"> I describe the modifications to the standard forward-shock model required to account for the X-ray light-curve features discovered by Swift in the early afterglow emission and propose that a delayed, pair-enriched, and highly relativistic outflow, which bulk-scatters the forward-shock synchrotron emission, yields sometimes a brighter X-ray emission, producing short-lived X-ray flares, X-ray light-curve plateaus ending with chromatic breaks, and fast post-plateau X-ray decays. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0802.1235v1-abstract-full').style.display = 'none'; document.getElementById('0802.1235v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 8 February, 2008; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> February 2008. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">6 pages, submitted to the proceedings of 2007 GRB meeting, Santa Fe, NM, Nov 5-9 2007</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> AIP Conf.Proc.1000:433-438,2008 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/0712.1536">arXiv:0712.1536</a> <span> [<a href="https://arxiv.org/pdf/0712.1536">pdf</a>, <a href="https://arxiv.org/ps/0712.1536">ps</a>, <a href="https://arxiv.org/format/0712.1536">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2008.12950.x">10.1111/j.1365-2966.2008.12950.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> GeV emission from Gamma-Ray Burst afterglows </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="0712.1536v2-abstract-short" style="display: inline;"> We calculate the GeV afterglow emission expected from a few mechanisms related to GRBs and their afterglows. Given the brightness of the early X-ray afterglow emission measured by Swift/XRT, GLAST/LAT should detect the self-Compton emission from the forward-shock driven by the GRB ejecta into the circumburst medium. Novel features discovered by Swift in X-ray afterglows (plateaus and chromatic l… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0712.1536v2-abstract-full').style.display = 'inline'; document.getElementById('0712.1536v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="0712.1536v2-abstract-full" style="display: none;"> We calculate the GeV afterglow emission expected from a few mechanisms related to GRBs and their afterglows. Given the brightness of the early X-ray afterglow emission measured by Swift/XRT, GLAST/LAT should detect the self-Compton emission from the forward-shock driven by the GRB ejecta into the circumburst medium. Novel features discovered by Swift in X-ray afterglows (plateaus and chromatic light-curve breaks) indicate the existence of a pair-enriched, relativistic outflow located behind the forward shock. Bulk and inverse-Compton upscattering of the prompt GRB emission by such outflows provide another source of GeV afterglow emission detectable by LAT. The large-angle burst emission and synchrotron forward-shock emission are, most likely, too dim at high photon energy to be observed by LAT. The spectral slope of the high-energy afterglow emission and its decay rate (if it can be measured) allow the identification of the mechanism producing the GeV transient emission following GRBs. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0712.1536v2-abstract-full').style.display = 'none'; document.getElementById('0712.1536v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 10 January, 2008; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 10 December, 2007; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> December 2007. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">8 pages, accepted by MNRAS</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Mon.Not.Roy.Astron.Soc. 385 (2008) 1628-1634 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/0708.1509">arXiv:0708.1509</a> <span> [<a href="https://arxiv.org/pdf/0708.1509">pdf</a>, <a href="https://arxiv.org/ps/0708.1509">ps</a>, <a href="https://arxiv.org/format/0708.1509">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2007.12607.x">10.1111/j.1365-2966.2007.12607.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> X-ray flares, plateaus, and chromatic breaks of GRB afterglows from up-scattered forward-shock emission </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="0708.1509v2-abstract-short" style="display: inline;"> Scattering of the forward-shock synchrotron emission by a relativistic outflow located behind the leading blast-wave may produce an X-ray emission brighter than that coming directly from the forward-shock and may explain four features displayed by Swift X-ray afterglows: flares, plateaus (slow decays), chromatic light-curve breaks, and fast post-plateau decays. For a cold scattering outflow, the… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0708.1509v2-abstract-full').style.display = 'inline'; document.getElementById('0708.1509v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="0708.1509v2-abstract-full" style="display: none;"> Scattering of the forward-shock synchrotron emission by a relativistic outflow located behind the leading blast-wave may produce an X-ray emission brighter than that coming directly from the forward-shock and may explain four features displayed by Swift X-ray afterglows: flares, plateaus (slow decays), chromatic light-curve breaks, and fast post-plateau decays. For a cold scattering outflow, the reflected flux overshines the primary one if the scattering outflow is nearly baryon-free and highly relativistic. These two requirements can be relaxed if the scattering outflow is energized by weak internal shocks, so that the incident forward-shock photons are also inverse-Compton scattered, in addition to bulk-scattering. Sweeping-up of the photons left behind by the forward shock naturally yields short X-ray flares. Owing to the boost in photon energy produced by bulk-scattering scattering, the reflected emission is more likely to overshine that coming directly from the forward shock at higher photon energies, yielding light-curve plateaus and breaks that appear only in the X-ray. The brightness, shape, and decay of the X-ray light-curve plateau depend on the radial distribution of the scatterer's Lorentz factor and mass-flux. Chromatic X-ray light-curve breaks and sharp post-plateau decays cannot be accommodated by the direct forward-shock emission and argue in favour of the scattering-outflow model proposed here. On the other hand, the X-ray afterglows without plateaus, those with achromatic breaks, and those with very long-lived power-law decays are more naturally accommodated by the standard forward-shock model. Thus the diversity of X-ray light-curves arises from the interplay of the scattered and direct forward-shock emissions. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0708.1509v2-abstract-full').style.display = 'none'; document.getElementById('0708.1509v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 17 October, 2007; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 10 August, 2007; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2007. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">to appear in MNRAS, 12 pages, 7 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Mon.Not.Roy.Astron.Soc. 383 (2008) 1143-1153 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/0705.1015">arXiv:0705.1015</a> <span> [<a href="https://arxiv.org/pdf/0705.1015">pdf</a>, <a href="https://arxiv.org/ps/0705.1015">ps</a>, <a href="https://arxiv.org/format/0705.1015">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2007.12084.x">10.1111/j.1365-2966.2007.12084.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Jet-breaks in the X-ray Light-Curves of Swift GRB Afterglows </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="0705.1015v2-abstract-short" style="display: inline;"> In the set of 236 GRB afterglows observed by Swift between January 2005 and March 2007, we identify 30 X-ray light-curves whose power-law fall-off exhibit a steepening ("break") at 0.1-10 day after trigger, to a decay steeper than t^{-1.5}. For most of these afterglows, the X-ray spectral slope and the decay indices before and after the break can be accommodated by the standard jet model althoug… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0705.1015v2-abstract-full').style.display = 'inline'; document.getElementById('0705.1015v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="0705.1015v2-abstract-full" style="display: none;"> In the set of 236 GRB afterglows observed by Swift between January 2005 and March 2007, we identify 30 X-ray light-curves whose power-law fall-off exhibit a steepening ("break") at 0.1-10 day after trigger, to a decay steeper than t^{-1.5}. For most of these afterglows, the X-ray spectral slope and the decay indices before and after the break can be accommodated by the standard jet model although a different origin of the breaks cannot be ruled out. In addition, there are 27 other afterglows whose X-ray light-curves may also exhibit a late break to a steep decay, but the evidence is not that compelling. The X-ray emissions of 38 afterglows decay slower than t^{-1.5} until after 3 day, half of them exhibiting such a slow decay until after 10 day. Therefore, the fraction of well-monitored Swift afterglows with potential jet-breaks is around 60 percent, whether we count only the strongest cases for each type or all of them. This fraction is comparable to the 75 percent of pre-Swift afterglows whose optical light-curves displayed similar breaks at ~1 day. The properties of the prompt emission of Swift afterglows with light-curve breaks show the same correlations (peak energy of GRB spectrum with the burst isotropic output and with burst collimated output) as previously found for pre-Swift optical afterglows with light-curve breaks (the Amati and Ghirlanda relations, respectively). However, we find that Ghirlanda relation is largely a consequence of Amati's and that the use of the jet-break time leads to a stronger Ghirlanda correlation only when the few outliers to the Amati relation are included. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('0705.1015v2-abstract-full').style.display = 'none'; document.getElementById('0705.1015v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 7 June, 2007; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 7 May, 2007; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2007. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">7 pages, accepted by MNRAS, afterglows with lower limits on jet-break time added to Amati & Ghirlanda relations</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Mon.Not.Roy.Astron.Soc.380:374-380,2007 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0702338">arXiv:astro-ph/0702338</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0702338">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0702338">ps</a>, <a href="https://arxiv.org/format/astro-ph/0702338">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1086/523768">10.1086/523768 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Constraints on Type Ib/c and GRB Progenitors </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Fryer%2C+C+L">C. L. Fryer</a>, <a href="/search/astro-ph?searchtype=author&query=Mazzali%2C+P+A">P. A. Mazzali</a>, <a href="/search/astro-ph?searchtype=author&query=Prochaska%2C+J">J. Prochaska</a>, <a href="/search/astro-ph?searchtype=author&query=Cappellaro%2C+E">E. Cappellaro</a>, <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Berger%2C+E">E. Berger</a>, <a href="/search/astro-ph?searchtype=author&query=van+Putten%2C+M">M. van Putten</a>, <a href="/search/astro-ph?searchtype=author&query=Heuvel%2C+E+P+J+v+d">E. P. J. van den Heuvel</a>, <a href="/search/astro-ph?searchtype=author&query=Young%2C+P">P. Young</a>, <a href="/search/astro-ph?searchtype=author&query=Hungerford%2C+A">A. Hungerford</a>, <a href="/search/astro-ph?searchtype=author&query=Rockefeller%2C+G">G. Rockefeller</a>, <a href="/search/astro-ph?searchtype=author&query=Yoon%2C+S+-">S. -C. Yoon</a>, <a href="/search/astro-ph?searchtype=author&query=Podsiadlowski%2C+P">P. Podsiadlowski</a>, <a href="/search/astro-ph?searchtype=author&query=Nomoto%2C+K">K. Nomoto</a>, <a href="/search/astro-ph?searchtype=author&query=Chevalier%2C+R">R. Chevalier</a>, <a href="/search/astro-ph?searchtype=author&query=Schmidt%2C+B">B. Schmidt</a>, <a href="/search/astro-ph?searchtype=author&query=Kulkarni%2C+S">S. Kulkarni</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0702338v1-abstract-short" style="display: inline;"> Although there is strong support for the collapsar engine as the power source of long-duration gamma-ray bursts (GRBs), we still do not definitively know the progenitor of these explosions. Here we review the current set of progenitor scenarios for long-duration GRBs and the observational constraints on these scenarios. Examining these, we find that single-star models cannot be the only progenit… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0702338v1-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0702338v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0702338v1-abstract-full" style="display: none;"> Although there is strong support for the collapsar engine as the power source of long-duration gamma-ray bursts (GRBs), we still do not definitively know the progenitor of these explosions. Here we review the current set of progenitor scenarios for long-duration GRBs and the observational constraints on these scenarios. Examining these, we find that single-star models cannot be the only progenitor for long-duration GRBs. Several binary progenitors can match the solid observational constraints and also have the potential to match the trends we are currently seeing in the observations. Type Ib/c supernovae are also likely to be produced primarily in binaries; we discuss the relationship between the progenitors of these explosions and those of the long-duration GRBs. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0702338v1-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0702338v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 13 February, 2007; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> February 2007. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">36 pages, 6 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Report number:</span> LAUR-07-0657 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0702319">arXiv:astro-ph/0702319</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0702319">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0702319">ps</a>, <a href="https://arxiv.org/format/astro-ph/0702319">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2007.00286.x">10.1111/j.1365-2966.2007.00286.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> The nature of the outflow in gamma-ray bursts </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Kumar%2C+P">P. Kumar</a>, <a href="/search/astro-ph?searchtype=author&query=McMahon%2C+E">E. McMahon</a>, <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Willingale%2C+R">R. Willingale</a>, <a href="/search/astro-ph?searchtype=author&query=O%27Brien%2C+P">P. O'Brien</a>, <a href="/search/astro-ph?searchtype=author&query=Burrows%2C+D">D. Burrows</a>, <a href="/search/astro-ph?searchtype=author&query=Cummings%2C+J">J. Cummings</a>, <a href="/search/astro-ph?searchtype=author&query=Gehrels%2C+N">N. Gehrels</a>, <a href="/search/astro-ph?searchtype=author&query=Holland%2C+S">S. Holland</a>, <a href="/search/astro-ph?searchtype=author&query=Pandey%2C+S+B">S. B. Pandey</a>, <a href="/search/astro-ph?searchtype=author&query=Berk%2C+D+V">D. Vanden Berk</a>, <a href="/search/astro-ph?searchtype=author&query=Zane%2C+S">S. Zane</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0702319v1-abstract-short" style="display: inline;"> The Swift satellite has enabled us to follow the evolution of gamma-ray burst (GRB) fireballs from the prompt gamma-ray emission to the afterglow phase. The early x-ray and optical data obtained by telescopes aboard the Swift satellite show that the source for prompt gamma-ray emission, the emission that heralds these bursts, is short lived and that its source is distinct from that of the ensuin… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0702319v1-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0702319v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0702319v1-abstract-full" style="display: none;"> The Swift satellite has enabled us to follow the evolution of gamma-ray burst (GRB) fireballs from the prompt gamma-ray emission to the afterglow phase. The early x-ray and optical data obtained by telescopes aboard the Swift satellite show that the source for prompt gamma-ray emission, the emission that heralds these bursts, is short lived and that its source is distinct from that of the ensuing, long-lived afterglow. Using these data, we determine the distance of the gamma-ray source from the center of the explosion. We find this distance to be 1e15-1e16 cm for most bursts and we show that this is within a factor of ten of the radius of the shock-heated circumstellar medium (CSM) producing the x-ray photons. Furthermore, using the early gamma-ray, x-ray and optical data, we show that the prompt gamma-ray emission cannot be produced in internal shocks, nor can it be produced in the external shock; in a more general sense gamma-ray generation mechanisms based on shock physics have problems explaining the GRB data for the ten Swift bursts analyzed in this work. A magnetic field dominated outflow model for GRBs has some attractive features, although the evidence in its favor is inconclusive. Finally, the x-ray and optical data allow us to provide an upper limit on the density of the CSM of about 10 protons per cubic cm at a distance of about 5e16 cm from the center of explosion. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0702319v1-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0702319v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 12 February, 2007; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> February 2007. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Accepted to MNRAS Letters. 6 pages, 2 figures, & 2 tables</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Mon.Not.Roy.Astron.Soc.Lett.376:L57-L61,2007 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0612504">arXiv:astro-ph/0612504</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0612504">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0612504">ps</a>, <a href="https://arxiv.org/format/astro-ph/0612504">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2007.11398.x">10.1111/j.1365-2966.2007.11398.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> A unified picture for the gamma-ray and prompt optical emissions of GRB 990123 </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Kumar%2C+P">P. Kumar</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0612504v1-abstract-short" style="display: inline;"> The prompt optical emission of GRB 990123 was uncorrelated to the gamma-ray light-curve and exhibited temporal properties similar to those of the steeply-decaying, early X-ray emission observed by Swift at the end of many bursts. These facts suggest that the optical counterpart of GRB 990123 was the large-angle emission released during (the second pulse of) the burst. If the optical and gamma-ra… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0612504v1-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0612504v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0612504v1-abstract-full" style="display: none;"> The prompt optical emission of GRB 990123 was uncorrelated to the gamma-ray light-curve and exhibited temporal properties similar to those of the steeply-decaying, early X-ray emission observed by Swift at the end of many bursts. These facts suggest that the optical counterpart of GRB 990123 was the large-angle emission released during (the second pulse of) the burst. If the optical and gamma-ray emissions of GRB 990123 have, indeed, the same origin then their properties require that (i) the optical counterpart was synchrotron emission and the gamma-rays arose from inverse-Compton scatterings ("synchrotron self-Compton model"), (ii) the peak-energy of the optical-synchrotron component was at ~20 eV, and (iii) the burst emission was produced by a relativistic outflow moving at Lorentz factor > 450 and at a radius > 10^{15} cm, which is comparable to the outflow deceleration radius. Because the spectrum of GRB 990123 was optically thin above 2 keV, the magnetic field behind the shock must have decayed on a length-scale of <1% of the thickness of the shocked gas, which corresponds to 10^6-10^7 plasma skin-depths. Consistency of the optical counterpart decay rate and its spectral slope (or that of the burst, if they represent different spectral components) with the expectations for the large-angle burst emission represents the most direct test of the unifying picture proposed here for GRB 990123. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0612504v1-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0612504v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 18 December, 2006; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> December 2006. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">9 pages, accepted for publication by MNRAS</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Mon.Not.Roy.Astron.Soc.376:1065-1072,2007 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0612170">arXiv:astro-ph/0612170</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0612170">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0612170">ps</a>, <a href="https://arxiv.org/format/astro-ph/0612170">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2007.11956.x">10.1111/j.1365-2966.2007.11956.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Swift GRB Afterglows and the Forward-Shock Model </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0612170v2-abstract-short" style="display: inline;"> The X-ray light-curves of the GRB afterglows monitored by Swift display one to four phases of power-law decay. In chronological order they are: the burst tail, the "hump", the standard decay, and the post jet-break decay. The large-angle emission produced during the burst, but arriving at observer later, is consistent with the GRB tail decay for less than half of bursts. The forward-shock sync… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0612170v2-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0612170v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0612170v2-abstract-full" style="display: none;"> The X-ray light-curves of the GRB afterglows monitored by Swift display one to four phases of power-law decay. In chronological order they are: the burst tail, the "hump", the standard decay, and the post jet-break decay. The large-angle emission produced during the burst, but arriving at observer later, is consistent with the GRB tail decay for less than half of bursts. The forward-shock synchrotron emission from a very narrow jet (half-angle less than 1 deg) is consistent with the decay of 75 percent of GRB tails. The forward-shock inverse-Compton emission from a narrow jet that does not expand sideways also accommodates the decay of 80 percent of GRB tails. The X-ray light-curve hump can be attributed to an increasing kinetic energy per solid angle of the forward-shock region visible to the observer. This increase could be due to the emergence of the emission from an outflow seen from a location outside its opening. However, the correlations among the hump timing, flux, and decay index expected in this model are not confirmed by observations. Thus, the increase in the forward-shock kinetic energy is more likely caused by some incoming ejecta arriving at the shock during the afterglow phase. The jet interpretation for the burst tails and the energy injection scenario for the hump lead to a double-jet outflow structure consisting of a narrow GRB jet which precedes a wider afterglow outflow of lower kinetic energy per solid angle but higher total energy. (X-ray light-curves are shown for GRB 050416A, 050525A, 050717, 050721, 050724, 050730, 050802, 051109A, 060124, 060206, 060526). <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0612170v2-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0612170v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 8 May, 2007; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 6 December, 2006; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> December 2006. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">accepted by MNRAS, 14 pages, 14 figures, additions: inverse-Compton emission for GRB tails (S2,fig3), implications for GRB efficiency (S3.1.3), achromatic breaks at ~1 hour (S4,fig10), GRB 060206 (S6,fig14)</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Mon.Not.Roy.Astron.Soc.379:331-342,2007 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0610570">arXiv:astro-ph/0610570</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0610570">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0610570">ps</a>, <a href="https://arxiv.org/format/astro-ph/0610570">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1051/0004-6361:20065173">10.1051/0004-6361:20065173 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Swift observations of GRB050904: the most distant cosmic explosion ever observed </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Cusumano%2C+G">G. Cusumano</a>, <a href="/search/astro-ph?searchtype=author&query=Mangano%2C+V">V. Mangano</a>, <a href="/search/astro-ph?searchtype=author&query=Chincarini%2C+G">G. Chincarini</a>, <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Burrows%2C+D+N">D. N. Burrows</a>, <a href="/search/astro-ph?searchtype=author&query=La+Parola%2C+V">V. La Parola</a>, <a href="/search/astro-ph?searchtype=author&query=Sakamoto%2C+T">T. Sakamoto</a>, <a href="/search/astro-ph?searchtype=author&query=Campana%2C+S">S. Campana</a>, <a href="/search/astro-ph?searchtype=author&query=Mineo%2C+T">T. Mineo</a>, <a href="/search/astro-ph?searchtype=author&query=Tagliaferri%2C+G">G. Tagliaferri</a>, <a href="/search/astro-ph?searchtype=author&query=Angelini%2C+L">L. Angelini</a>, <a href="/search/astro-ph?searchtype=author&query=Barthelemy%2C+S+D">S. D. Barthelemy</a>, <a href="/search/astro-ph?searchtype=author&query=Beardmore%2C+A+P">A. P. Beardmore</a>, <a href="/search/astro-ph?searchtype=author&query=Boyd%2C+P+T">P. T. Boyd</a>, <a href="/search/astro-ph?searchtype=author&query=Cominsky%2C+L">L. Cominsky</a>, <a href="/search/astro-ph?searchtype=author&query=Gronwall%2C+C">C. Gronwall</a>, <a href="/search/astro-ph?searchtype=author&query=Fenimore%2C+E+E">E. E. Fenimore</a>, <a href="/search/astro-ph?searchtype=author&query=Gehrels%2C+N">N. Gehrels</a>, <a href="/search/astro-ph?searchtype=author&query=Giommi%2C+P">P. Giommi</a>, <a href="/search/astro-ph?searchtype=author&query=Goad%2C+M">M. Goad</a>, <a href="/search/astro-ph?searchtype=author&query=Hurley%2C+K">K. Hurley</a>, <a href="/search/astro-ph?searchtype=author&query=Immler%2C+S">S. Immler</a>, <a href="/search/astro-ph?searchtype=author&query=Kennea%2C+J+A">J. A. Kennea</a>, <a href="/search/astro-ph?searchtype=author&query=Mason%2C+K+O">K. O. Mason</a>, <a href="/search/astro-ph?searchtype=author&query=Marshall%2C+F">F. Marshall</a> , et al. (8 additional authors not shown) </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0610570v2-abstract-short" style="display: inline;"> Swift discovered the high redshift (z=6.29) GRB050904 with the Burst Alert Telescope (BAT) and began observing with its narrow field instruments 161 s after the burst onset. This gamma-ray burst is the most distant cosmic explosion ever observed. Because of its high redshift, the X-ray Telescope (XRT) and BAT simultaneous observations provide 4 orders of magnitude of spectral coverage (0.2-150 k… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0610570v2-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0610570v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0610570v2-abstract-full" style="display: none;"> Swift discovered the high redshift (z=6.29) GRB050904 with the Burst Alert Telescope (BAT) and began observing with its narrow field instruments 161 s after the burst onset. This gamma-ray burst is the most distant cosmic explosion ever observed. Because of its high redshift, the X-ray Telescope (XRT) and BAT simultaneous observations provide 4 orders of magnitude of spectral coverage (0.2-150 keV; 1.4-1090 keV in the source rest frame) at a very early source-frame time (22 s). GRB050904 was a long, multi-peaked, bright GRB with strong variability during its entire evolution. The light curve observed by the XRT is characterized by the presence of a long flaring activity lasting up to 1-2 hours after the burst onset in the burst rest frame, with no evidence of a smooth power-law decay following the prompt emission as seen in other GRBs. However, the BAT tail extrapolated to the XRT band joins the XRT early light curve and the overall behavior resembles that of a very long GRB prompt. The spectral energy distribution softens with time, with the photon index decreasing from -1.2 during the BAT observation to -1.9 at the end of the XRT observation. The dips of the late X-ray flares may be consistent with an underlying X-ray emission arising from the forward shock and with the properties of the optical afterglow reported by Tagliaferri et al. (2005b). We interpret the BAT and XRT data as a single continuous observation of the prompt emission from a very long GRB. The peculiarities observed in GRB050904 could be due to its origin within one of the first star-forming regions in the Universe; very low metallicities of the progenitor at these epochs may provide an explanation. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0610570v2-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0610570v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 8 November, 2006; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 18 October, 2006; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> October 2006. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">9 pages, 2 table, 6 figures, accepted for publication on A&A</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Astron.Astrophys.462:73,2007 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0607396">arXiv:astro-ph/0607396</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0607396">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0607396">ps</a>, <a href="https://arxiv.org/format/astro-ph/0607396">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1393/ncb/i2007-10066-7">10.1393/ncb/i2007-10066-7 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Phases of Swift X-ray Afterglows </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0607396v2-abstract-short" style="display: inline;"> The X-ray afterglows observed by Swift exhibit rich light-curves, with four phases of different decay rate. The temporal and spectral properties for a set of 47 bursts are used to identify the mechanisms which can explain these four phases. The early, fast-decaying phase can be attributed to the same mechanism which generated the burst emission (internal shocks in a relativistic outflow), while… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0607396v2-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0607396v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0607396v2-abstract-full" style="display: none;"> The X-ray afterglows observed by Swift exhibit rich light-curves, with four phases of different decay rate. The temporal and spectral properties for a set of 47 bursts are used to identify the mechanisms which can explain these four phases. The early, fast-decaying phase can be attributed to the same mechanism which generated the burst emission (internal shocks in a relativistic outflow), while the following phases of slower decay can be identified with synchrotron emission from the forward shock sweeping the circumburst medium. Most likely, the phase of slowest decay is due to a continuous energy injection in the forward shock. That the optical power-law decay continues unabated after the end of energy injection requires an ambient medium with a wind-like density structure (n propto r^{-2}) and forward shock microphysical parameters that change with the shock's Lorentz factor. A later break of the X-ray light-curve can be attributed to a collimated outflow whose boundary becomes visible to the observer (a jet) but the optical and X-ray decays are not always consistent with the standard jet model expectations. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0607396v2-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0607396v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 13 November, 2006; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 17 July, 2006; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> July 2006. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">17 pages. First half will appear in Il Nuovo Cimento ("Swift and GRBs: unveiling the relativistic Universe" meeting, Venice, Italy, 5-9 June 2006). Second half will appear in AIP Conf. Procs. ("Multicoloured landscape of compact objects" meeting, Cefalu, Italy, 11-24 June 2006)</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Nuovo Cim.B121:1099-1104,2006 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0604320">arXiv:astro-ph/0604320</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0604320">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0604320">ps</a>, <a href="https://arxiv.org/format/astro-ph/0604320">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1086/508740">10.1086/508740 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Jet Breaks in Short Gamma-Ray Bursts. II: The Collimated Afterglow of GRB 051221A </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Burrows%2C+D+N">David N. Burrows</a>, <a href="/search/astro-ph?searchtype=author&query=Grupe%2C+D">Dirk Grupe</a>, <a href="/search/astro-ph?searchtype=author&query=Capalbi%2C+M">Milvia Capalbi</a>, <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">Alin Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Patel%2C+S+K">Sandeep K. Patel</a>, <a href="/search/astro-ph?searchtype=author&query=Kouveliotou%2C+C">Chryssa Kouveliotou</a>, <a href="/search/astro-ph?searchtype=author&query=Zhang%2C+B">Bing Zhang</a>, <a href="/search/astro-ph?searchtype=author&query=Meszaros%2C+P">Peter Meszaros</a>, <a href="/search/astro-ph?searchtype=author&query=Chincarini%2C+G">Guido Chincarini</a>, <a href="/search/astro-ph?searchtype=author&query=Gehrels%2C+N">N. Gehrels</a>, <a href="/search/astro-ph?searchtype=author&query=Wijers%2C+R+A+M">Ralph A. M. Wijers</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0604320v2-abstract-short" style="display: inline;"> We report the best evidence to date of a jet break in a short Gamma-Ray Burst (GRB) afterglow, using Chandra and Swift XRT observations of the X-ray afterglow of GRB 051221A. The combined X-ray light curve, which has three breaks, is similar to those commonly observed in Swift observations of long GRBs. A flat segment of the light curve at ~0.1 days after the burst represents the first clear cas… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0604320v2-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0604320v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0604320v2-abstract-full" style="display: none;"> We report the best evidence to date of a jet break in a short Gamma-Ray Burst (GRB) afterglow, using Chandra and Swift XRT observations of the X-ray afterglow of GRB 051221A. The combined X-ray light curve, which has three breaks, is similar to those commonly observed in Swift observations of long GRBs. A flat segment of the light curve at ~0.1 days after the burst represents the first clear case of strong energy injection in the external shock of a short GRB afterglow. The last break occurs at ~4 days post-burst and breaks to a power-law decay index of ~2. We interpret this as a jet break, with important implications for models of short GRBs, since it requires collimation of the afterglow into a jet with an initial opening angle ~4-8 degrees and implies a total jet kinetic energy of E_jet ~(1-5) x 10^{49} erg. Combined with the lack of a jet break in GRB 050724, this suggests a wide range in jet collimation in short GRBs, with at least some having collimation similar to that found in long GRBs, though with significantly lower jet energies. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0604320v2-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0604320v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 30 August, 2006; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 13 April, 2006; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2006. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">10 pages, 4 figures. Submitted to The Astrophysical Journal 13 April 2006, accepted 7 August 2006. This revision is the accepted version</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Astrophys.J.653:468-473,2006 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0604105">arXiv:astro-ph/0604105</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0604105">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0604105">ps</a>, <a href="https://arxiv.org/format/astro-ph/0604105">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2006.10453.x">10.1111/j.1365-2966.2006.10453.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Evidence for chromatic X-ray light-curve breaks in Swift GRB afterglows and their theoretical implications </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Meszaros%2C+P">P. Meszaros</a>, <a href="/search/astro-ph?searchtype=author&query=Burrows%2C+D">D. Burrows</a>, <a href="/search/astro-ph?searchtype=author&query=Nousek%2C+J">J. Nousek</a>, <a href="/search/astro-ph?searchtype=author&query=Gehrels%2C+N">N. Gehrels</a>, <a href="/search/astro-ph?searchtype=author&query=O%27Brien%2C+P">P. O'Brien</a>, <a href="/search/astro-ph?searchtype=author&query=Willingale%2C+R">R. Willingale</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0604105v1-abstract-short" style="display: inline;"> The power-law decay of the X-ray emission of GRB afterglows 050319, 050401, 050607, 050713A, 050802 and 050922C exhibits a steepening at about 1--4 hours after the burst which, surprisingly, is not accompanied by a break in the optical emission. If it is assumed that both the optical and X-ray afterglows arise from the same outflow then, in the framework of the standard forward shock model, the… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0604105v1-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0604105v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0604105v1-abstract-full" style="display: none;"> The power-law decay of the X-ray emission of GRB afterglows 050319, 050401, 050607, 050713A, 050802 and 050922C exhibits a steepening at about 1--4 hours after the burst which, surprisingly, is not accompanied by a break in the optical emission. If it is assumed that both the optical and X-ray afterglows arise from the same outflow then, in the framework of the standard forward shock model, the chromaticity of the X-ray light-curve breaks indicates that they do not arise solely from a mechanism related to the outflow dynamics (e.g. energy injection) or the angular distribution of the blast-wave kinetic energy (structured outflows or jets). The lack of a spectral evolution accompanying the X-ray light-curve breaks shows that these breaks do not arise from the passage of a spectral break (e.g. the cooling frequency) either. Under these circumstances, the decoupling of the X-ray and optical decays requires that the microphysical parameters for the electron and magnetic energies in the forward shock evolve in time, whether the X-ray afterglow is synchrotron or inverse-Compton emission. For a steady evolution of these parameters with the Lorentz factor of the forward shock and an X-ray light-curve break arising from cessation of energy injection into the blast-wave, the optical and X-ray properties of the above six Swift afterglows require a circumburst medium with a r^{-2} radial stratification, as expected for a massive star origin for long GRBs. Alternatively, the chromatic X-ray light-curve breaks may indicate that the optical and X-ray emissions arise from different outflows. Neither feature (evolution of microphysical parameters or the different origin of the optical and X-ray emissions) were clearly required by pre-Swift afterglows. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0604105v1-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0604105v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 5 April, 2006; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2006. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">6 pages, sumbitted to MNRAS</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Mon.Not.Roy.Astron.Soc.369:2059,2006 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0511588">arXiv:astro-ph/0511588</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0511588">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0511588">ps</a>, <a href="https://arxiv.org/format/astro-ph/0511588">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1745-3933.2005.00134.x">10.1111/j.1745-3933.2005.00134.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> The Energetics and Environment of the Short-GRB Afterglows 050709 and 050724 </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0511588v1-abstract-short" style="display: inline;"> We use the available radio, optical and X-ray measurements for the afterglows of the short bursts 050709 and 050724 to constrain the blast-wave energy, its collimation and the density of the circumburst medium. For GRB 050709 (whose duration was 0.07 s), we identify two models: i) a high-density solution, where the ejecta are collimated in a jet of half-angle theta_{jet} > 6 deg and interact wit… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0511588v1-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0511588v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0511588v1-abstract-full" style="display: none;"> We use the available radio, optical and X-ray measurements for the afterglows of the short bursts 050709 and 050724 to constrain the blast-wave energy, its collimation and the density of the circumburst medium. For GRB 050709 (whose duration was 0.07 s), we identify two models: i) a high-density solution, where the ejecta are collimated in a jet of half-angle theta_{jet} > 6 deg and interact with a medium of particle density 10^{-4}/cc < n < 0.1/cc, and ii) a low-density solution with theta_{jet} > 2 deg and n < 10^{-5}/cc. These density ranges are compatible with those expected in the vicinity of the host galaxy and in the intergalactic medium, lending support to the hypothesis that the progenitor of GRB 050907 is a NS-NS or NS-BH merger. For GRB 050724 (which last 3 s), we obtain 0.1/cc < n < 1000/cc and theta_{jet} > 8 deg. The range of allowed densities shows that this burst occurred in the intragalactic environment. The dynamical parameters of the high-density model for the GRB afterglow 050709 are similar to those for 050724. If these parameters are representative for short-GRB outflows, then these jets are less collimated and have a lower kinetic energy than those of long bursts, which suggests that GRB jets are not magnetically collimated and are powered by the gravitational energy of the torus. Evidently, the analysis of more short-GRB afterglows is required for a more robust conclusion. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0511588v1-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0511588v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 18 November, 2005; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> November 2005. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">5 pages, submitted to MNRAS</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Mon.Not.Roy.Astron.Soc.Lett.367:L42-L46,2006 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0511576">arXiv:astro-ph/0511576</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0511576">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0511576">ps</a>, <a href="https://arxiv.org/format/astro-ph/0511576">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1086/499432">10.1086/499432 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Discovery of an Afterglow Extension of the Prompt Phase of Two Gamma Ray Bursts Observed by Swift </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Barthelmy%2C+S+D">S. D. Barthelmy</a>, <a href="/search/astro-ph?searchtype=author&query=Cannizzo%2C+J+K">J. K. Cannizzo</a>, <a href="/search/astro-ph?searchtype=author&query=Gehrels%2C+N">N. Gehrels</a>, <a href="/search/astro-ph?searchtype=author&query=Cusumano%2C+G">G. Cusumano</a>, <a href="/search/astro-ph?searchtype=author&query=Mangano%2C+V">V. Mangano</a>, <a href="/search/astro-ph?searchtype=author&query=O%27Brien%2C+P+T">P. T. O'Brien</a>, <a href="/search/astro-ph?searchtype=author&query=Vaughan%2C+S">S. Vaughan</a>, <a href="/search/astro-ph?searchtype=author&query=Zhang%2C+B">B. Zhang</a>, <a href="/search/astro-ph?searchtype=author&query=Burrows%2C+D+N">D. N. Burrows</a>, <a href="/search/astro-ph?searchtype=author&query=Campana%2C+S">S. Campana</a>, <a href="/search/astro-ph?searchtype=author&query=Chincarini%2C+G">G. Chincarini</a>, <a href="/search/astro-ph?searchtype=author&query=Goad%2C+M+R">M. R. Goad</a>, <a href="/search/astro-ph?searchtype=author&query=Kouveliotou%2C+C">C. Kouveliotou</a>, <a href="/search/astro-ph?searchtype=author&query=Kumar%2C+P">P. Kumar</a>, <a href="/search/astro-ph?searchtype=author&query=Meszaros%2C+P">P. Meszaros</a>, <a href="/search/astro-ph?searchtype=author&query=Nousek%2C+J+A">J. A. Nousek</a>, <a href="/search/astro-ph?searchtype=author&query=Osborne%2C+J+P">J. P. Osborne</a>, <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Reeves%2C+J+N">J. N. Reeves</a>, <a href="/search/astro-ph?searchtype=author&query=Sakamoto%2C+T">T. Sakamoto</a>, <a href="/search/astro-ph?searchtype=author&query=Tagliaferri%2C+G">G. Tagliaferri</a>, <a href="/search/astro-ph?searchtype=author&query=Wijers%2C+R+A+M+J">R. A. M. J. Wijers</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0511576v1-abstract-short" style="display: inline;"> BAT and XRT observations of two recent well-covered GRBs observed by Swift, GRB 050315 and GRB 050319, show clearly a prompt component joining the onset of the afterglow emission. By fitting a power law form to the gamma-ray spectrum, we extrapolate the time dependent fluxes measured by the BAT, in the energy band 15-350 keV, into the spectral regime observed by the XRT 0.2-10 keV, and examine t… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0511576v1-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0511576v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0511576v1-abstract-full" style="display: none;"> BAT and XRT observations of two recent well-covered GRBs observed by Swift, GRB 050315 and GRB 050319, show clearly a prompt component joining the onset of the afterglow emission. By fitting a power law form to the gamma-ray spectrum, we extrapolate the time dependent fluxes measured by the BAT, in the energy band 15-350 keV, into the spectral regime observed by the XRT 0.2-10 keV, and examine the functional form of the rate of decay of the two light curves. We find that the BAT and XRT light curves merge to form a unified curve. There is a period of steep decay up to ~300 s, followed by a flatter decay. The duration of the steep decay, ~100 s in the source frame after correcting for cosmological time dilation, agrees roughly with a theoretical estimate for the deceleration time of the relativistic ejecta as it interacts with circumstellar material. For GRB 050315, the steep decay can be characterized by an exponential form, where one e-folding decay time t_e(BAT) ~ 24+/-2 s, and t_e(XRT) ~ 35+/-2 s. For GRB 050319, a power law decay -(d ln f/d ln t) = n, where n is about 3, provides a reasonable fit. The early time X-ray fluxes are consistent with representing the lower energy tail of the prompt emission, and provide our first quantitative measure of the decay of the prompt gamma-ray emission over a large dynamic range in flux. The initial steep decay is expected due to the delayed high latitude photons from a curved shell of relativistic plasma illuminated only for a short interval. The overall conclusion is that the prompt phase of GRBs remains observable for hundreds of seconds longer than previously thought. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0511576v1-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0511576v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 18 November, 2005; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> November 2005. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">4 pages, 2 Postscript figures, uses revsymb.sty, emulateapj.cls, revtex4.cls, aps.rtx, 10pt.rtx. Astrophysical Journal Letters (in press)</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Astrophys.J.635:L133-L136,2005 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0509737">arXiv:astro-ph/0509737</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0509737">pdf</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1038/440164a">10.1038/440164a <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Detection of a huge explosion in the early Universe </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Cusumano%2C+G">G. Cusumano</a>, <a href="/search/astro-ph?searchtype=author&query=Mangano%2C+V">V. Mangano</a>, <a href="/search/astro-ph?searchtype=author&query=Chincarini%2C+G">G. Chincarini</a>, <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Burrows%2C+D+N">D. N. Burrows</a>, <a href="/search/astro-ph?searchtype=author&query=La+Parola%2C+V">V. La Parola</a>, <a href="/search/astro-ph?searchtype=author&query=Sakamoto%2C+T">T. Sakamoto</a>, <a href="/search/astro-ph?searchtype=author&query=Campana%2C+S">S. Campana</a>, <a href="/search/astro-ph?searchtype=author&query=Mineo%2C+T">T. Mineo</a>, <a href="/search/astro-ph?searchtype=author&query=Tagliaferri%2C+G">G. Tagliaferri</a>, <a href="/search/astro-ph?searchtype=author&query=Angelini%2C+L">L. Angelini</a>, <a href="/search/astro-ph?searchtype=author&query=Barthelemy%2C+S+D">S. D. Barthelemy</a>, <a href="/search/astro-ph?searchtype=author&query=Beardmore%2C+A+P">A. P. Beardmore</a>, <a href="/search/astro-ph?searchtype=author&query=Boyd%2C+P+T">P. T. Boyd</a>, <a href="/search/astro-ph?searchtype=author&query=Cominsky%2C+L">L. Cominsky</a>, <a href="/search/astro-ph?searchtype=author&query=Gronwall%2C+C">C. Gronwall</a>, <a href="/search/astro-ph?searchtype=author&query=Fenimore%2C+E+E">E. E. Fenimore</a>, <a href="/search/astro-ph?searchtype=author&query=Gehrels%2C+N">N. Gehrels</a>, <a href="/search/astro-ph?searchtype=author&query=Giommi%2C+P">P. Giommi</a>, <a href="/search/astro-ph?searchtype=author&query=Goad%2C+M">M. Goad</a>, <a href="/search/astro-ph?searchtype=author&query=Hurley%2C+K">K. Hurley</a>, <a href="/search/astro-ph?searchtype=author&query=Kennea%2C+J+A">J. A. Kennea</a>, <a href="/search/astro-ph?searchtype=author&query=Mason%2C+K+O">K. O. Mason</a>, <a href="/search/astro-ph?searchtype=author&query=Marshall%2C+F">F. Marshall</a>, <a href="/search/astro-ph?searchtype=author&query=Meszaros%2C+P">P. Meszaros</a> , et al. (7 additional authors not shown) </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0509737v5-abstract-short" style="display: inline;"> Gamma-ray Bursts (GRBs) are bright flashes of high energy photons that can last from about 10 milliseconds to 10 minutes. Their origin and nature have puzzled the scientific community for about 25 years until 1997, when the first X-ray afterglows of long (> 2 s duration) bursts were detected and the first optical and radio counterparts were found. These measurements established that long GRBs ar… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0509737v5-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0509737v5-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0509737v5-abstract-full" style="display: none;"> Gamma-ray Bursts (GRBs) are bright flashes of high energy photons that can last from about 10 milliseconds to 10 minutes. Their origin and nature have puzzled the scientific community for about 25 years until 1997, when the first X-ray afterglows of long (> 2 s duration) bursts were detected and the first optical and radio counterparts were found. These measurements established that long GRBs are typically at high redshift (z 1.6) and are in sub-luminous star-forming host galaxies. They are likely produced in core-collapse explosions of a class of massive stars that give rise to highly relativistic jets (collapsar model). Internal inhomogeneities in the velocity field of the relativistic expanding flow lead to collisions between fast moving and slow moving fluid shells and to the formation of internal shock waves. These shocks are believed to produce the observed prompt emission in the form of irregularly shaped and spaced pulses of gamma-rays, each pulse corresponding to a distinct internal collision. The expansion of the jet outward into the circumstellar medium is believed to give rise to ``external'' shocks, responsible for producing the smoothly fading afterglow emission seen in the X-ray, optical and radio bands. Here we report on the gamma-ray and x-ray observation of the most distant gamma-ray burst ever observed: its redshift of 6.29 translates to a distance of 13 billion light-years from Earth, corresponding to a time when the Universe was just 700 million to 750 million years old. The discovery of a gamma-ray burst at such a large redshift implies the presence of massive stars only 700 million years after the Big Bang. The very high redshift bursts represent a good way to study the re-ionization era soon after the Universe came out of the Dark Ages. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0509737v5-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0509737v5-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 23 March, 2006; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 24 September, 2005; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2005. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">11 pages, 1 table, 3 figures. Note: this paper has been submitted for publication in Nature, It is embargoed for discussion in the popular press</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0508426">arXiv:astro-ph/0508426</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0508426">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0508426">ps</a>, <a href="https://arxiv.org/format/astro-ph/0508426">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2005.09532.x">10.1111/j.1365-2966.2005.09532.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Jets, Structured Outflows, and Energy Injection in GRB Afterglows: Numerical Modelling </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0508426v1-abstract-short" style="display: inline;"> We investigate numerically the ability of three models (jet, structured outflow, energy injection) to accommodate the optical light-curve breaks observed in 10 GRB afterglows (980519, 990123, 990510, 991216, 000301c, 000926, 010222, 011211, 020813, and 030226), and the relative intensities of the radio, optical, and X-ray emissions of these afterglows. We find that the jet and structured outflow… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0508426v1-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0508426v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0508426v1-abstract-full" style="display: none;"> We investigate numerically the ability of three models (jet, structured outflow, energy injection) to accommodate the optical light-curve breaks observed in 10 GRB afterglows (980519, 990123, 990510, 991216, 000301c, 000926, 010222, 011211, 020813, and 030226), and the relative intensities of the radio, optical, and X-ray emissions of these afterglows. We find that the jet and structured outflow models fare much better than the energy injection model in accommodating the multiwavelength data of the above 10 afterglows. For the first two models, a uniform circumburst medium provides a better fit to the optical light-curve break than a wind-like medium with a r^{-2} stratification. However, in the only two cases where the energy injection model may be at work, a wind medium is favoured (an energy injection is also possible in a third case, the afterglow 970508, whose optical emission exhibited a sharp rise but not a steepening decay). The best fit parameters obtained with the jet model indicate an outflow energy of 2-6 E50 ergs and a jet opening of 2-3 degrees. Structured outflows with a quasi-uniform core have a core angular size of 0.7-1.0 degrees and an energy per solid angle of 0.5-3 E53 erg/sr, surrounded by an envelope where this energy falls-off roughly as theta^{-2} with angle from the outflow axis, requiring thus the same energy budget as jets. Circumburst densities are found to be typically in the range 0.1-1 per cc, for either model. We also find that the reverse shock emission resulting from the injection of ejecta into the decelerating blast wave at about 1 day after the burst can explain the slowly decaying radio light-curves observed for the afterglows 990123, 991216, and 010222. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0508426v1-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0508426v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 19 August, 2005; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2005. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">17 pages, to be published in the MNRAS</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Mon.Not.Roy.Astron.Soc.363:1409-1423,2005 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0508340">arXiv:astro-ph/0508340</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0508340">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0508340">ps</a>, <a href="https://arxiv.org/format/astro-ph/0508340">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2005.09900.x">10.1111/j.1365-2966.2005.09900.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Analysis of the X-ray Emission of Nine Swift Afterglows </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Meszaros%2C+P">P. Meszaros</a>, <a href="/search/astro-ph?searchtype=author&query=Gehrels%2C+N">N. Gehrels</a>, <a href="/search/astro-ph?searchtype=author&query=Burrows%2C+D">D. Burrows</a>, <a href="/search/astro-ph?searchtype=author&query=Nousek%2C+J">J. Nousek</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0508340v2-abstract-short" style="display: inline;"> The X-ray light-curves of 9 Swift XRT afterglows (050126, 050128, 050219A, 050315, 050318, 050319, 050401, 050408, 050505) display a complex behaviour: a steep t^{-3.0 \pm 0.3} decay until ~400 s, followed by a significantly slower t^{-0.65+/-0.20} fall-off, which at 0.2--2 d after the burst evolves into a t^{-1.7+/-0.5} decay. We consider three possible models for the geometry of relativistic b… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0508340v2-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0508340v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0508340v2-abstract-full" style="display: none;"> The X-ray light-curves of 9 Swift XRT afterglows (050126, 050128, 050219A, 050315, 050318, 050319, 050401, 050408, 050505) display a complex behaviour: a steep t^{-3.0 \pm 0.3} decay until ~400 s, followed by a significantly slower t^{-0.65+/-0.20} fall-off, which at 0.2--2 d after the burst evolves into a t^{-1.7+/-0.5} decay. We consider three possible models for the geometry of relativistic blast-waves (spherical outflows, non-spreading jets, and spreading jets), two possible dynamical regimes for the forward shock (adiabatic and fully radiative), and we take into account a possible angular structure of the outflow and delayed energy injection in the blast-wave, to identify the models which reconcile the X-ray light-curve decay with the slope of the X-ray continuum for each of the above three afterglow phases. By piecing together the various models for each phase in a way that makes physical sense, we identify possible models for the entire X-ray afterglow. The major conclusion of this work is that a long-lived episode of energy injection in the blast-wave, during which the shock energy increases at t^{1.0+/-0.5}, is required for five afterglows and could be at work in the other four as well. Optical observations in conjunction with the X-ray can distinguish among these various models. Our simple tests allow the determination of the location of the cooling frequency relative to the X-ray domain and, thus, of the index of the electron power-law distribution with energy in the blast-wave. The resulting indices are clearly inconsistent with an universal value. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0508340v2-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0508340v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 23 November, 2005; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 15 August, 2005; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2005. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">10 pages, minor changes, to be published in the MNRAS</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Mon.Not.Roy.Astron.Soc.366:1357-1366,2006 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0506577">arXiv:astro-ph/0506577</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0506577">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0506577">ps</a>, <a href="https://arxiv.org/format/astro-ph/0506577">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2005.09352.x">10.1111/j.1365-2966.2005.09352.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Models for Achromatic Light-Curve Breaks in GRB Afterglows: Jets, Structured Outflows, and Energy Injection </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0506577v1-abstract-short" style="display: inline;"> The steepening (break) of the power-law fall-off observed in the optical emission of some GRB afterglows at epoch ~1 day is often attributed to a collimated outflow (jet), undergoing lateral spreading. Wider opening GRB ejecta with a non-uniform energy angular distribution (structured outflows) or the cessation of energy injection in the afterglow can also yield light-curve breaks. We determine… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0506577v1-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0506577v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0506577v1-abstract-full" style="display: none;"> The steepening (break) of the power-law fall-off observed in the optical emission of some GRB afterglows at epoch ~1 day is often attributed to a collimated outflow (jet), undergoing lateral spreading. Wider opening GRB ejecta with a non-uniform energy angular distribution (structured outflows) or the cessation of energy injection in the afterglow can also yield light-curve breaks. We determine the optical and X-ray light-curve decay indices and spectral energy distribution slopes for 10 GRB afterglows with optical light-curve breaks (980519, 990123, 990510, 991216, 000301, 000926, 010222, 011211, 020813, 030226), and use these properties to test the above models for light-curve steepening. It is found that the optical breaks of six of these afterglows can be accommodated by either energy injection or by structured outflows. In the refreshed shock model, a wind-like stratification of the circumburst medium (as expected for massive stars as GRB progenitors) is slightly favoured. A spreading jet interacting with a homogeneous circumburst medium is required by the afterglows 990510, 000301, 011211, and 030226. The optical pre- and post-break decays of these four afterglows are incompatible with a wind-like medium. The current sample of 10 afterglows with breaks suggests that the distribution of the break magnitude (defined as the increase of the afterglow decay exponent) is bimodal, with a gap at 1. If true, this bimodality favours the structured outflow model, while the gap location indicates a homogeneous circumburst environment. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0506577v1-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0506577v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 23 June, 2005; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> June 2005. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">11 pages, to be published in the MNRAS</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Mon.Not.Roy.Astron.Soc.362:921-930,2005 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0406027">arXiv:astro-ph/0406027</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0406027">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0406027">ps</a>, <a href="https://arxiv.org/format/astro-ph/0406027">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2004.08083.x">10.1111/j.1365-2966.2004.08083.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Analysis of Two Scenarios for the Early Optical Emission of the GRB Afterglows 990123 and 021211 </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Kumar%2C+P">P. Kumar</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0406027v1-abstract-short" style="display: inline;"> The optical light-curves of GRB afterglows 990123 and 021211 exhibit a steep decay at 100--600 seconds after the burst, the decay becoming slower after about 10 minutes. We investigate two scenarios for the fast decaying early optical emission of these GRB afterglows. In the reverse-forward shock scenario, this emission arises in the reverse shock crossing the GRB ejecta, the mitigation of the l… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0406027v1-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0406027v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0406027v1-abstract-full" style="display: none;"> The optical light-curves of GRB afterglows 990123 and 021211 exhibit a steep decay at 100--600 seconds after the burst, the decay becoming slower after about 10 minutes. We investigate two scenarios for the fast decaying early optical emission of these GRB afterglows. In the reverse-forward shock scenario, this emission arises in the reverse shock crossing the GRB ejecta, the mitigation of the light-curve decay occurring when the forward shock emission overtakes that from the reverse shock. Both a homogeneous and wind-like circumburst medium are considered. In the wind-bubble scenario, the steeply decaying, early optical emission arises from the forward shock interacting with a 1/r^2 bubble, with a negligible contribution from the reverse shock, the slower decay starting when the blast wave reaches the bubble termination shock and enters a homogeneous region of the circumburst medium. We determine the shock microphysical parameters, ejecta kinetic energy, and circumburst density which accommodate the radio and optical measurements of the GRB afterglows 990123 and 021211. We find that, for a homogeneous medium, the radio and optical emissions of the afterglow 990123 can be accommodated by the reverse-forward shock scenario if the microphysical parameters behind the two shocks differ substantially. A wind-like circumburst medium also allows the reverse-forward shocks scenario to account for the radio and optical properties of the afterglows 990123 and 021211, but the required wind densities are at least 10 times smaller than those of Galactic Wolf-Rayet stars. The wind-bubble scenario requires a variation of the microphysical parameters when the afterglow fireball reaches the wind termination shock, which seems a contrived feature. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0406027v1-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0406027v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 1 June, 2004; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> June 2004. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">13 pages, MNRAS, in press</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Mon.Not.Roy.Astron.Soc. 353 (2004) 511-522 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0404588">arXiv:astro-ph/0404588</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0404588">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0404588">ps</a>, <a href="https://arxiv.org/format/astro-ph/0404588">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2004.08245.x">10.1111/j.1365-2966.2004.08245.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Prompt Gamma-ray and Early Afterglow Emission in the External Shock Model </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=McMahon%2C+E">E. McMahon</a>, <a href="/search/astro-ph?searchtype=author&query=Kumar%2C+P">P. Kumar</a>, <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0404588v2-abstract-short" style="display: inline;"> We describe our attempt to determine if gamma-ray burst (GRB) and afterglow emissions could both arise in external shocks for simple GRBs--bursts consisting of just a few peaks in their lightcurves. We calculate peak flux and peak frequency during the gamma-ray burst for ten well observed bursts using the same set of parameters that are determined from modeling afterglow emissions. We find the g… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0404588v2-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0404588v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0404588v2-abstract-full" style="display: none;"> We describe our attempt to determine if gamma-ray burst (GRB) and afterglow emissions could both arise in external shocks for simple GRBs--bursts consisting of just a few peaks in their lightcurves. We calculate peak flux and peak frequency during the gamma-ray burst for ten well observed bursts using the same set of parameters that are determined from modeling afterglow emissions. We find the gamma-ray emission properties for 970508 (which had a single peak lightcurve) fit nicely with the extrapolation of its afterglow data, and therefore this burst was likely produced in the external shock. One can explain two other bursts in this sample as forward shock synchrotron emission provided that the magnetic field parameter during the burst is close to equipartition, and larger by a factor of 100 than the afterglow value at ~1 day. The remaining seven bursts cannot be explained in the external shock model even if we allow the energy fraction in electrons and magnetic field and the density of the surrounding medium to take on any physically permitted value; the peak of the spectrum is above the cooling frequency, therefore the peak flux is independent of the latter of these two parameters, and is too small by about an order of magnitude than the observed values. We have also considered inverse-Compton scattering in forward and reverse shock regions and find that it can explain the gamma-ray emission for a few bursts, but requires the density to be 1--2 orders of magnitude larger than a typical Wolf-Rayet star wind and much larger than permitted by late afterglow observations. [Abridged] <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0404588v2-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0404588v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 22 July, 2004; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 29 April, 2004; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2004. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Accepted to MNRAS, 10 pages</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0402119">arXiv:astro-ph/0402119</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0402119">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0402119">ps</a>, <a href="https://arxiv.org/format/astro-ph/0402119">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1063/1.1810886">10.1063/1.1810886 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> On the Shallow Decay of Some GRB Afterglows </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Kumar%2C+P">P. Kumar</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0402119v1-abstract-short" style="display: inline;"> Half of the radio afterglows for which there is a good temporal coverage exhibit after 10 days from the burst a decay which is shallower than at optical frequencies, contrary to what is expected within the simplest form of the standard model of relativistic fireballs or jets. We investigate possible ways to decouple the radio and optical decays. First, the radio and optical emissions are assumed… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0402119v1-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0402119v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0402119v1-abstract-full" style="display: none;"> Half of the radio afterglows for which there is a good temporal coverage exhibit after 10 days from the burst a decay which is shallower than at optical frequencies, contrary to what is expected within the simplest form of the standard model of relativistic fireballs or jets. We investigate possible ways to decouple the radio and optical decays. First, the radio and optical emissions are assumed to arise from the same electron population and we allow for either a time-varying slope of the power-law distribution of electron energy or for time-varying microphysical parameters. Then we consider two scenarios where the radio and optical emissions arise in distinct parts of the GRB outflow, either because the outflow has an angular structure or because there is a long-lived reverse shock. We find that the only the last scenario is compatible with the observations. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0402119v1-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0402119v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 4 February, 2004; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> February 2004. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">5 pages, to appear in Proc. of 2003 GRB Santa Fe Conference, this is a very short version of astro-ph/0308273</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0309161">arXiv:astro-ph/0309161</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0309161">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0309161">ps</a>, <a href="https://arxiv.org/format/astro-ph/0309161">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2004.08185.x">10.1111/j.1365-2966.2004.08185.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Creation of Electron--Positron Wind in Gamma-Ray Bursts and Its Effect on the Early Afterglow Emission </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Kumar%2C+P">P. Kumar</a>, <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0309161v1-abstract-short" style="display: inline;"> We calculate the creation of electron--positron pairs in Gamma-Ray Bursts (GRBs) resulting from the collision between scattered and outward moving gamma-ray photons. The number of pairs exceeds the number of ambient medium electrons encountered by the GRB ejecta up to ~ 10^{16} cm from the center of explosion. The shock resulting from the interaction of the ejecta with the pair-wind may brighten… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0309161v1-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0309161v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0309161v1-abstract-full" style="display: none;"> We calculate the creation of electron--positron pairs in Gamma-Ray Bursts (GRBs) resulting from the collision between scattered and outward moving gamma-ray photons. The number of pairs exceeds the number of ambient medium electrons encountered by the GRB ejecta up to ~ 10^{16} cm from the center of explosion. The shock resulting from the interaction of the ejecta with the pair-wind may brighten the afterglow synchrotron emission during the first few minutes. Even without this effect, the peak intensity of the optical afterglow increases with the density of the surrounding medium. Therefore, observations of the optical flux at early times constrain the density of the circumburst medium. If the electron and magnetic field energies behind the forward shock sweeping-up the pair-wind and the circumburst medium are as inferred from fits to the broadband afterglow emission at 0.5-100 days, then the current upper limits on the optical counterpart emission, set by the ROTSE and LOTIS experiments, indicate that the circumburst medium within 0.01 pc is less dense than 100 cm^{-3} or, if a wind, corresponds to a progenitor mass-loss to wind speed ratio below 10^{-6} M_sun/yr/(1000 km/s). <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0309161v1-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0309161v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 4 September, 2003; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2003. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">9 pages, submitted to MNRAS in 2002</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Mon.Not.Roy.Astron.Soc.354:252-258,2004 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0308273">arXiv:astro-ph/0308273</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0308273">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0308273">ps</a>, <a href="https://arxiv.org/format/astro-ph/0308273">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2004.07635.x">10.1111/j.1365-2966.2004.07635.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> The Slow Decay of Some Radio Afterglows, a Puzzle for the Simplest GRB Fireball Model </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Kumar%2C+P">P. Kumar</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0308273v2-abstract-short" style="display: inline;"> Abridged: The decay of half of the GRB radio afterglows with long temporal monitoring is significantly slower than at optical frequencies, contrary to what is expected in the simplest fireball model. We investigate four ways to decouple the radio and optical decays: an evolving index of the power-law distribution of the shock-accelerated electrons, the presence of a spectral break between the t… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0308273v2-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0308273v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0308273v2-abstract-full" style="display: none;"> Abridged: The decay of half of the GRB radio afterglows with long temporal monitoring is significantly slower than at optical frequencies, contrary to what is expected in the simplest fireball model. We investigate four ways to decouple the radio and optical decays: an evolving index of the power-law distribution of the shock-accelerated electrons, the presence of a spectral break between the two domains, a structured outflow, and a long-lived reverse shock contribution to the afterglow emission. [...] In the fourth scenario, it is assumed that the radio afterglow emission arises in the reverse shock propagating in a steady stream of ejecta, which catch up with the decelerating GRB remnant. This scenario can accommodate the properties of the afterglows with slow radio decays and requires that the injected energy is less than or comparable to the initial fireball energy, while other afterglow parameters have reasonable values. For a jet, the transition to a semi-relativistic motion mitigates the radio decay, however this scenario would work only when the slower radio decay is observed well after the steeper optical fall-off. A structured outflow with a relativistic core, yielding a fast decaying optical emission, and a non-relativistic envelope, producing a slowly falling-off radio afterglow, is not a viable solution, as it fails to decouple the radio and optical decays. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0308273v2-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0308273v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 4 February, 2004; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 15 August, 2003; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2003. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">to appear in MNRAS, 20 pages, added section on a long-lived reverse shock as possible explanation of the slow radio afterglows</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Mon.Not.Roy.Astron.Soc.350:213,2004 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0305446">arXiv:astro-ph/0305446</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0305446">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0305446">ps</a>, <a href="https://arxiv.org/format/astro-ph/0305446">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1111/j.1365-2966.2003.07138.x">10.1111/j.1365-2966.2003.07138.x <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> A Unified Treatment of the Gamma-Ray Burst 021211 and Its Afterglow Emissions </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Kumar%2C+P">Pawan Kumar</a>, <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">Alin Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0305446v2-abstract-short" style="display: inline;"> The Gamma-Ray Burst (GRB) 021211 detected by the High Energy Transient Explorer (HETE) II had a simple light-curve in the x-ray and gamma-ray energy bands containing one peak and little temporal fluctuation other than the expected Poisson variation. Such a burst offers the best chance for a unified understanding of the gamma-ray burst and afterglow emissions. We provide a detailed modeling of th… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0305446v2-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0305446v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0305446v2-abstract-full" style="display: none;"> The Gamma-Ray Burst (GRB) 021211 detected by the High Energy Transient Explorer (HETE) II had a simple light-curve in the x-ray and gamma-ray energy bands containing one peak and little temporal fluctuation other than the expected Poisson variation. Such a burst offers the best chance for a unified understanding of the gamma-ray burst and afterglow emissions. We provide a detailed modeling of the observed radiation from GRB 021211 both during the burst and the afterglow phase. The consistency between early optical emission (prior to 11 minutes), which presumably comes from reverse shock heating of the ejecta, and late afterglow emission from forward shock (later than 11 minutes) requires the energy density in the magnetic field in the ejecta, expressed as fraction of the equipartition value or $蔚_B$, to be larger than the forward shock at 11 minutes by a factor of about 10$^3$. We find that the only consistent model for the gamma-ray emission in GRB 021211 is the synchrotron radiation in the forward shock; to explain the peak flux during the GRB requires $蔚_B$ in forward shock at deceleration to be larger than the value at 11 minutes by a factor of about 10$^2$. These results suggest that the magnetic field in the reverse shock and early forward shock is most likely frozen-in-field from the explosion, and therefore a large fraction of the energy in the explosion was initially stored in magnetic field. We can rule out the possibility that the ejecta from the burst for GRB 021211 contained more than 10 electron-positron pairs per proton. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0305446v2-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0305446v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 23 May, 2003; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 22 May, 2003; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2003. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">25 pages, 2 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Mon.Not.Roy.Astron.Soc. 346 (2003) 905 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0301032">arXiv:astro-ph/0301032</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0301032">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0301032">ps</a>, <a href="https://arxiv.org/format/astro-ph/0301032">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1086/375563">10.1086/375563 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> The Effect of Angular Structure of Gamma-Ray Burst Outflows on the Afterglow Emission </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Kumar%2C+P">P. Kumar</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0301032v2-abstract-short" style="display: inline;"> We investigate analytically the effect of an anisotropic distribution of the kinetic energy within a relativistic fireball on the decay of the afterglow emission, focusing on axially symmetric fireballs with a uniform core and a power-law decrease with angle outside the core. The afterglow fall-off steepens after the core becomes fully visible. For observer directions within the core, simple for… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0301032v2-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0301032v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0301032v2-abstract-full" style="display: none;"> We investigate analytically the effect of an anisotropic distribution of the kinetic energy within a relativistic fireball on the decay of the afterglow emission, focusing on axially symmetric fireballs with a uniform core and a power-law decrease with angle outside the core. The afterglow fall-off steepens after the core becomes fully visible. For observer directions within the core, simple formulae are derived for the afterglow decay after the break, while for off-core observers results are shown graphically. Some criteria for assessing from observations the necessity of an angular structure and/or collimation are given. Applying them to several afterglows with light-curve breaks, we find that jets endowed with structure are required only if the circumburst medium has a wind-like (r^{-2}) stratification. Numerical fits to the multiwavelength emission of the afterglows 990510 and 000301c show that, for the former, the angular distribution of the ejecta kinetic energy is not far from uniformity, and that, with a standard power-law electron distribution, the sharp steepening of the R-band light-curve of the latter is better accommodated by a structured jet than an uniform outflow. Structured outflows may accommodate the shallower light-curve breaks observed in other afterglows. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0301032v2-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0301032v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 27 March, 2003; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 2 January, 2003; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> January 2003. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">accepted by ApJ, analytical treatment in S2 shortened, references added, 11 pages, color figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Astrophys.J. 592 (2003) 390-400 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0211189">arXiv:astro-ph/0211189</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0211189">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0211189">ps</a>, <a href="https://arxiv.org/format/astro-ph/0211189">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1086/373896">10.1086/373896 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> GRB 021004: a Massive Progenitor Star Surrounded by Shells </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Schaefer%2C+B+E">Bradley E. Schaefer</a>, <a href="/search/astro-ph?searchtype=author&query=Gerardy%2C+C+L">C. L. Gerardy</a>, <a href="/search/astro-ph?searchtype=author&query=Hoflich%2C+P">P. Hoflich</a>, <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">A. Panaitescu</a>, <a href="/search/astro-ph?searchtype=author&query=Quimby%2C+R">R. Quimby</a>, <a href="/search/astro-ph?searchtype=author&query=Mader%2C+J">J. Mader</a>, <a href="/search/astro-ph?searchtype=author&query=Hill%2C+G+J">G. J. Hill</a>, <a href="/search/astro-ph?searchtype=author&query=Kumar%2C+P">P. Kumar</a>, <a href="/search/astro-ph?searchtype=author&query=Wheeler%2C+J+C">J. C. Wheeler</a>, <a href="/search/astro-ph?searchtype=author&query=Eracleous%2C+M">M. Eracleous</a>, <a href="/search/astro-ph?searchtype=author&query=Sigurdsson%2C+S">S. Sigurdsson</a>, <a href="/search/astro-ph?searchtype=author&query=Meszaros%2C+P">P. Meszaros</a>, <a href="/search/astro-ph?searchtype=author&query=Zhang%2C+B">B. Zhang</a>, <a href="/search/astro-ph?searchtype=author&query=Wang%2C+L">L. Wang</a>, <a href="/search/astro-ph?searchtype=author&query=Hessman%2C+F">F. Hessman</a>, <a href="/search/astro-ph?searchtype=author&query=Petrosian%2C+V">V. Petrosian</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0211189v2-abstract-short" style="display: inline;"> We present spectra of the optical transient of GRB021004 obtained with the Hobby-Eberly telescope starting 15.48, 20.31 hours, and 4.84 days after the burst and a spectrum obtained with the H. J. Smith 2.7 m Telescope starting 14.31 hours after the burst. GRB021004 is the first afterglow whose spectrum is dominated by absorption lines from high ionization species with multiple velocity component… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0211189v2-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0211189v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0211189v2-abstract-full" style="display: none;"> We present spectra of the optical transient of GRB021004 obtained with the Hobby-Eberly telescope starting 15.48, 20.31 hours, and 4.84 days after the burst and a spectrum obtained with the H. J. Smith 2.7 m Telescope starting 14.31 hours after the burst. GRB021004 is the first afterglow whose spectrum is dominated by absorption lines from high ionization species with multiple velocity components separated by up to 3000 km/s. We argue that these lines are likely to come from shells around a massive progenitor star. The high velocities and high ionizations arise from a combination of acceleration and flash-ionization by the burst photons and the wind velocity and steady ionization by the progenitor. We also analyze the broad-band spectrum and the light curve. We distinguish six components along the line of sight: (1) The z~2.293 absorption lines arise from the wind of a massive star. For a mass loss rate of ~6 x 10^{-5} solar masses per year, this component also provides the external medium to create the afterglow light. (2) A second shell produces absorption lines with a relative velocity of 560 km/s, and this is associated with the shell created by the fast massive star wind blowing a bubble in the preceding slow wind at a radial distance of order 10 pc. (3) More distant clouds within the host galaxy lie between 30-2500 pc, where they have been ionized by the burst. (4-6) The massive star wind has clumps with radii and over-densities of 0.022, 0.063, and 0.12 parsecs and 50%, 10%, and 10% respectively. The immediate progenitor of the burster could either be a WC-type Wolf-Rayet star or a highly evolved star whose original mass was just too small for it to become a WN-type Wolf-Rayet star. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0211189v2-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0211189v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 18 February, 2003; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 9 November, 2002; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> November 2002. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">citations added, moderate changes, 31 pages, 4 figures, Ap.J. in press (v588, May 1, 2003)</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Astrophys.J. 588 (2003) 387-399 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/astro-ph/0204258">arXiv:astro-ph/0204258</a> <span> [<a href="https://arxiv.org/pdf/astro-ph/0204258">pdf</a>, <a href="https://arxiv.org/ps/astro-ph/0204258">ps</a>, <a href="https://arxiv.org/format/astro-ph/0204258">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics">astro-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1086/341738">10.1086/341738 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Orphan Afterglows of Collimated Gamma-Ray Bursts: Rate Predictions and Prospects for Detection </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Totani%2C+T">Tomonori Totani</a>, <a href="/search/astro-ph?searchtype=author&query=Panaitescu%2C+A">Alin Panaitescu</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="astro-ph/0204258v2-abstract-short" style="display: inline;"> We make a quantitative prediction for the detection rate of orphan GRB afterglows as a function of flux sensitivity in X-ray, optical, and radio wavebands, based on a recent model of collimated GRB afterglows. We find that the orphan afterglow rate strongly depends on the opening angle of the jet (roughly \propto 胃_jet^{-2}), as expected from simple geometrical consideration, if the total jet en… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0204258v2-abstract-full').style.display = 'inline'; document.getElementById('astro-ph/0204258v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="astro-ph/0204258v2-abstract-full" style="display: none;"> We make a quantitative prediction for the detection rate of orphan GRB afterglows as a function of flux sensitivity in X-ray, optical, and radio wavebands, based on a recent model of collimated GRB afterglows. We find that the orphan afterglow rate strongly depends on the opening angle of the jet (roughly \propto 胃_jet^{-2}), as expected from simple geometrical consideration, if the total jet energy is kept constant as suggested by recent studies. The relative beaming factor b_rel, i.e., the ratio of all afterglow rate including orphans to those associated with observable prompt GRBs, could be as high as b_rel >~ 100 for searches deeper than R ~ 24, depending on afterglow parameters. To make the most plausible predictions, we average the model emission for ten sets of afterglow parameters obtained through fits to ten well-observed, collimated GRB jets, weighted by the sky coverage of each jet. Our model expectations are consistent with the results (or constraints) obtained by all past searches. We estimate the number of orphan afterglows in the first 1500deg^2 field of the SDSS to be about 0.2. The relative beaming factor b_rel is rapidly increasing with the search sensitivity: b_rel ~ 3 for the SDSS sensitivity to transient objects in the northern sky (R ~ 19), ~14 for the past high-z supernova searches (R ~ 23), and ~50 for the sensitivity of the Subaru Suprime-Cam (R ~ 26). Predictions are made for the current facilities and future projects in X-ray, optical, and radio bands. Among them, the southern-sky observation of the SDSS (sensitive to transients down to R ~ 23) could detect ~40 orphan afterglows during the five-year operation. Allen Telescope Array would find about 200 afterglows in a radio band at ~0.1-1mJy with b_rel ~ 15. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('astro-ph/0204258v2-abstract-full').style.display = 'none'; document.getElementById('astro-ph/0204258v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 9 May, 2002; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 16 April, 2002; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2002. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Accepted to ApJ after minor changes. The afterglow sample is extended, and the predicted numbers are changed but only slightly. Received Apr 5, Accepted May 8</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Astrophys.J. 576 (2002) 120-134 </p> </li> </ol> <nav class="pagination is-small is-centered breathe-horizontal" role="navigation" aria-label="pagination"> <a href="" class="pagination-previous is-invisible">Previous </a> <a href="/search/?searchtype=author&query=Panaitescu%2C+A&start=50" class="pagination-next" >Next </a> <ul class="pagination-list"> <li> <a href="/search/?searchtype=author&query=Panaitescu%2C+A&start=0" class="pagination-link is-current" aria-label="Goto page 1">1 </a> </li> <li> <a href="/search/?searchtype=author&query=Panaitescu%2C+A&start=50" class="pagination-link " aria-label="Page 2" aria-current="page">2 </a> </li> </ul> </nav> <div class="is-hidden-tablet">  <span class="help" style="display: inline-block;"><a href="https://github.com/arXiv/arxiv-search/releases">Search v0.5.6 released 2020-02-24</a>  </span> 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