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<button class="button is-small is-link">Go</button> </div> </div> </form> </div> </div> <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/2412.06644">arXiv:2412.06644</a> <span> [<a href="https://arxiv.org/pdf/2412.06644">pdf</a>, <a href="https://arxiv.org/format/2412.06644">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"> "Bursts, Beats, and Beyond": Uncovering the landscape from accretion to ignition of 4U 1728-34 using AstroSat </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Salgundi%2C+A">Anirudh Salgundi</a>, <a href="/search/astro-ph?searchtype=author&query=Bala%2C+S">Suman Bala</a>, <a href="/search/astro-ph?searchtype=author&query=Raman%2C+G">Gayathri Raman</a>, <a href="/search/astro-ph?searchtype=author&query=Pathak%2C+U">Utkarsh Pathak</a>, <a href="/search/astro-ph?searchtype=author&query=Bhalerao%2C+V">Varun Bhalerao</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="2412.06644v2-abstract-short" style="display: inline;"> A comprehensive study on persistent and thermonuclear burst emission of 4U 1728-34, commonly known as 'Slow Burster' is performed using seven archival observations of AstroSat spanning from 2016-2019. The burst-free persistent spectra can be well fitted with a blackbody (bbody) and a powerlaw (powerlaw) components, with a powerlaw photon index (Gamma) was found to be ~2 indicating the source was i… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2412.06644v2-abstract-full').style.display = 'inline'; document.getElementById('2412.06644v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2412.06644v2-abstract-full" style="display: none;"> A comprehensive study on persistent and thermonuclear burst emission of 4U 1728-34, commonly known as 'Slow Burster' is performed using seven archival observations of AstroSat spanning from 2016-2019. The burst-free persistent spectra can be well fitted with a blackbody (bbody) and a powerlaw (powerlaw) components, with a powerlaw photon index (Gamma) was found to be ~2 indicating the source was in "high/soft" bananna state or intermediate state. The time averaged power density spectrum reveals the presence of twin kilohertz Quasi Periodic Oscillations (kHz QPOs) with centroid frequencies 619+/-10 Hz and 965+/-6 Hz with a maximum fractional root mean squared amplitude of 6.24+/-1.31% at ~16 keV. From the upper kHz QPO, we infer the magnetospheric disk radius to be ~17 km, corresponding to a magnetic field strength of 0.35-1.27 * 10^7 G. The burst spectral evolution indicates Photospheric Radius Expansion (PRE) in five bursts, yeilding a touchdown radius of 3.1-5.47 km. These bursts reached near-Eddington luminosities, through which the distance of the source was calculated to be 5.18-5.21 kpc. Two of the bursts show coherent oscillations at 362.81-363.93 Hz. The presence of twin kHz QPOs and coherent Burst Oscillations allows us to provide two different estimates for the spin frequency of the Neutron Star in the system, for the first time using AstroSat. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2412.06644v2-abstract-full').style.display = 'none'; document.getElementById('2412.06644v2-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> 11 December, 2024; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 9 December, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> December 2024. </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">18 pages, 13 Figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2407.12867">arXiv:2407.12867</a> <span> [<a href="https://arxiv.org/pdf/2407.12867">pdf</a>, <a href="https://arxiv.org/format/2407.12867">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> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> </div> <p class="title is-5 mathjax"> Swift-BAT GUANO follow-up of gravitational-wave triggers in the third LIGO-Virgo-KAGRA observing run </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Raman%2C+G">Gayathri Raman</a>, <a href="/search/astro-ph?searchtype=author&query=Ronchini%2C+S">Samuele Ronchini</a>, <a href="/search/astro-ph?searchtype=author&query=Delaunay%2C+J">James Delaunay</a>, <a href="/search/astro-ph?searchtype=author&query=Tohuvavohu%2C+A">Aaron Tohuvavohu</a>, <a href="/search/astro-ph?searchtype=author&query=Kennea%2C+J+A">Jamie A. Kennea</a>, <a href="/search/astro-ph?searchtype=author&query=Parsotan%2C+T">Tyler Parsotan</a>, <a href="/search/astro-ph?searchtype=author&query=Ambrosi%2C+E">Elena Ambrosi</a>, <a href="/search/astro-ph?searchtype=author&query=Bernardini%2C+M+G">Maria Grazia Bernardini</a>, <a href="/search/astro-ph?searchtype=author&query=Campana%2C+S">Sergio Campana</a>, <a href="/search/astro-ph?searchtype=author&query=Cusumano%2C+G">Giancarlo Cusumano</a>, <a href="/search/astro-ph?searchtype=author&query=D%27Ai%2C+A">Antonino D'Ai</a>, <a href="/search/astro-ph?searchtype=author&query=D%27Avanzo%2C+P">Paolo D'Avanzo</a>, <a href="/search/astro-ph?searchtype=author&query=D%27Elia%2C+V">Valerio D'Elia</a>, <a href="/search/astro-ph?searchtype=author&query=De+Pasquale%2C+M">Massimiliano De Pasquale</a>, <a href="/search/astro-ph?searchtype=author&query=Dichiara%2C+S">Simone Dichiara</a>, <a href="/search/astro-ph?searchtype=author&query=Evans%2C+P">Phil Evans</a>, <a href="/search/astro-ph?searchtype=author&query=Hartmann%2C+D">Dieter Hartmann</a>, <a href="/search/astro-ph?searchtype=author&query=Kuin%2C+P">Paul Kuin</a>, <a href="/search/astro-ph?searchtype=author&query=Melandri%2C+A">Andrea Melandri</a>, <a href="/search/astro-ph?searchtype=author&query=O%27Brien%2C+P">Paul O'Brien</a>, <a href="/search/astro-ph?searchtype=author&query=Osborne%2C+J+P">Julian P. Osborne</a>, <a href="/search/astro-ph?searchtype=author&query=Page%2C+K">Kim Page</a>, <a href="/search/astro-ph?searchtype=author&query=Palmer%2C+D+M">David M. Palmer</a>, <a href="/search/astro-ph?searchtype=author&query=Sbarufatti%2C+B">Boris Sbarufatti</a>, <a href="/search/astro-ph?searchtype=author&query=Tagliaferri%2C+G">Gianpiero Tagliaferri</a> , et al. (1797 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="2407.12867v1-abstract-short" style="display: inline;"> We present results from a search for X-ray/gamma-ray counterparts of gravitational-wave (GW) candidates from the third observing run (O3) of the LIGO-Virgo-KAGRA (LVK) network using the Swift Burst Alert Telescope (Swift-BAT). The search includes 636 GW candidates received in low latency, 86 of which have been confirmed by the offline analysis and included in the third cumulative Gravitational-Wav… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2407.12867v1-abstract-full').style.display = 'inline'; document.getElementById('2407.12867v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2407.12867v1-abstract-full" style="display: none;"> We present results from a search for X-ray/gamma-ray counterparts of gravitational-wave (GW) candidates from the third observing run (O3) of the LIGO-Virgo-KAGRA (LVK) network using the Swift Burst Alert Telescope (Swift-BAT). The search includes 636 GW candidates received in low latency, 86 of which have been confirmed by the offline analysis and included in the third cumulative Gravitational-Wave Transient Catalogs (GWTC-3). Targeted searches were carried out on the entire GW sample using the maximum--likelihood NITRATES pipeline on the BAT data made available via the GUANO infrastructure. We do not detect any significant electromagnetic emission that is temporally and spatially coincident with any of the GW candidates. We report flux upper limits in the 15-350 keV band as a function of sky position for all the catalog candidates. For GW candidates where the Swift-BAT false alarm rate is less than 10$^{-3}$ Hz, we compute the GW--BAT joint false alarm rate. Finally, the derived Swift-BAT upper limits are used to infer constraints on the putative electromagnetic emission associated with binary black hole mergers. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2407.12867v1-abstract-full').style.display = 'none'; document.getElementById('2407.12867v1-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 July, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> July 2024. </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">50 pages, 10 figures, 4 tables</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2405.10752">arXiv:2405.10752</a> <span> [<a href="https://arxiv.org/pdf/2405.10752">pdf</a>, <a href="https://arxiv.org/format/2405.10752">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> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> </div> <p class="title is-5 mathjax"> Constraining possible $纬$-ray burst emission from GW230529 using Swift-BAT and Fermi-GBM </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Ronchini%2C+S">Samuele Ronchini</a>, <a href="/search/astro-ph?searchtype=author&query=Bala%2C+S">Suman Bala</a>, <a href="/search/astro-ph?searchtype=author&query=Wood%2C+J">Joshua Wood</a>, <a href="/search/astro-ph?searchtype=author&query=Delaunay%2C+J">James Delaunay</a>, <a href="/search/astro-ph?searchtype=author&query=Dichiara%2C+S">Simone Dichiara</a>, <a href="/search/astro-ph?searchtype=author&query=Kennea%2C+J+A">Jamie A. Kennea</a>, <a href="/search/astro-ph?searchtype=author&query=Parsotan%2C+T">Tyler Parsotan</a>, <a href="/search/astro-ph?searchtype=author&query=Raman%2C+G">Gayathri Raman</a>, <a href="/search/astro-ph?searchtype=author&query=Tohuvavohu%2C+A">Aaron Tohuvavohu</a>, <a href="/search/astro-ph?searchtype=author&query=Adhikari%2C+N">Naresh Adhikari</a>, <a href="/search/astro-ph?searchtype=author&query=Bhat%2C+N+P">Narayana P. Bhat</a>, <a href="/search/astro-ph?searchtype=author&query=Biscoveanu%2C+S">Sylvia Biscoveanu</a>, <a href="/search/astro-ph?searchtype=author&query=Bissaldi%2C+E">Elisabetta Bissaldi</a>, <a href="/search/astro-ph?searchtype=author&query=Burns%2C+E">Eric Burns</a>, <a href="/search/astro-ph?searchtype=author&query=Campana%2C+S">Sergio Campana</a>, <a href="/search/astro-ph?searchtype=author&query=Chandra%2C+K">Koustav Chandra</a>, <a href="/search/astro-ph?searchtype=author&query=Cleveland%2C+W+H">William H. Cleveland</a>, <a href="/search/astro-ph?searchtype=author&query=Dalessi%2C+S">Sarah Dalessi</a>, <a href="/search/astro-ph?searchtype=author&query=De+Pasquale%2C+M">Massimiliano De Pasquale</a>, <a href="/search/astro-ph?searchtype=author&query=Garc%C3%ADa-Bellido%2C+J">Juan Garc铆a-Bellido</a>, <a href="/search/astro-ph?searchtype=author&query=Gasbarra%2C+C">Claudio Gasbarra</a>, <a href="/search/astro-ph?searchtype=author&query=Giles%2C+M+M">Misty M. Giles</a>, <a href="/search/astro-ph?searchtype=author&query=Gupta%2C+I">Ish Gupta</a>, <a href="/search/astro-ph?searchtype=author&query=Hartmann%2C+D">Dieter Hartmann</a>, <a href="/search/astro-ph?searchtype=author&query=Hristov%2C+B+A">Boyan A. Hristov</a> , et al. (13 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="2405.10752v1-abstract-short" style="display: inline;"> GW230529 is the first compact binary coalescence detected by the LIGO-Virgo-KAGRA collaboration with at least one component mass confidently in the lower mass-gap, corresponding to the range 3-5$M_{\odot}$. If interpreted as a neutron star-black hole merger, this event has the most symmetric mass ratio detected so far and therefore has a relatively high probability of producing electromagnetic (EM… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2405.10752v1-abstract-full').style.display = 'inline'; document.getElementById('2405.10752v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2405.10752v1-abstract-full" style="display: none;"> GW230529 is the first compact binary coalescence detected by the LIGO-Virgo-KAGRA collaboration with at least one component mass confidently in the lower mass-gap, corresponding to the range 3-5$M_{\odot}$. If interpreted as a neutron star-black hole merger, this event has the most symmetric mass ratio detected so far and therefore has a relatively high probability of producing electromagnetic (EM) emission. However, no EM counterpart has been reported. At the merger time $t_0$, Swift-BAT and Fermi-GBM together covered 100$\%$ of the sky. Performing a targeted search in a time window $[t_0-20 \text{s},t_0+20 \text{s}]$, we report no detection by the Swift-BAT and the Fermi-GBM instruments. Combining the position-dependent $纬-$ray flux upper limits and the gravitational-wave posterior distribution of luminosity distance, sky localization and inclination angle of the binary, we derive constraints on the characteristic luminosity and structure of the jet possibly launched during the merger. Assuming a top-hat jet structure, we exclude at 90$\%$ credibility the presence of a jet which has at the same time an on-axis isotropic luminosity $\gtrsim 10^{48}$ erg s$^{-1}$, in the bolometric band 1 keV-10 MeV, and a jet opening angle $\gtrsim 15$ deg. Similar constraints are derived testing other assumptions about the jet structure profile. Excluding GRB 170817A, the luminosity upper limits derived here are below the luminosity of any GRB observed so far. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2405.10752v1-abstract-full').style.display = 'none'; document.getElementById('2405.10752v1-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 May, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2024. </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">18 pages, 1 table, 11 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2404.16425">arXiv:2404.16425</a> <span> [<a href="https://arxiv.org/pdf/2404.16425">pdf</a>, <a href="https://arxiv.org/format/2404.16425">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"> Soft X-ray prompt emission from a high-redshift gamma-ray burst EP240315a </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Liu%2C+Y">Y. Liu</a>, <a href="/search/astro-ph?searchtype=author&query=Sun%2C+H">H. Sun</a>, <a href="/search/astro-ph?searchtype=author&query=Xu%2C+D">D. Xu</a>, <a href="/search/astro-ph?searchtype=author&query=Svinkin%2C+D+S">D. S. Svinkin</a>, <a href="/search/astro-ph?searchtype=author&query=Delaunay%2C+J">J. Delaunay</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=Gao%2C+H">H. Gao</a>, <a href="/search/astro-ph?searchtype=author&query=Zhang%2C+C">C. Zhang</a>, <a href="/search/astro-ph?searchtype=author&query=Chen%2C+Y">Y. Chen</a>, <a href="/search/astro-ph?searchtype=author&query=Wu%2C+X+-">X. -F. Wu</a>, <a href="/search/astro-ph?searchtype=author&query=Zhang%2C+B">B. Zhang</a>, <a href="/search/astro-ph?searchtype=author&query=Yuan%2C+W">W. Yuan</a>, <a href="/search/astro-ph?searchtype=author&query=An%2C+J">J. An</a>, <a href="/search/astro-ph?searchtype=author&query=Bruni%2C+G">G. Bruni</a>, <a href="/search/astro-ph?searchtype=author&query=Frederiks%2C+D+D">D. D. Frederiks</a>, <a href="/search/astro-ph?searchtype=author&query=Ghirlanda%2C+G">G. Ghirlanda</a>, <a href="/search/astro-ph?searchtype=author&query=Hu%2C+J+-">J. -W. Hu</a>, <a href="/search/astro-ph?searchtype=author&query=Li%2C+A">A. Li</a>, <a href="/search/astro-ph?searchtype=author&query=Li%2C+C+-">C. -K. Li</a>, <a href="/search/astro-ph?searchtype=author&query=Li%2C+J+-">J. -D. Li</a>, <a href="/search/astro-ph?searchtype=author&query=Malesani%2C+D+B">D. B. Malesani</a>, <a href="/search/astro-ph?searchtype=author&query=Piro%2C+L">L. Piro</a>, <a href="/search/astro-ph?searchtype=author&query=Raman%2C+G">G. Raman</a>, <a href="/search/astro-ph?searchtype=author&query=Ricci%2C+R">R. Ricci</a>, <a href="/search/astro-ph?searchtype=author&query=Troja%2C+E">E. Troja</a> , et al. (170 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="2404.16425v1-abstract-short" style="display: inline;"> Long gamma-ray bursts (GRBs) are believed to originate from core collapse of massive stars. High-redshift GRBs can probe the star formation and reionization history of the early universe, but their detection remains rare. Here we report the detection of a GRB triggered in the 0.5--4 keV band by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated as EP240315a,… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2404.16425v1-abstract-full').style.display = 'inline'; document.getElementById('2404.16425v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2404.16425v1-abstract-full" style="display: none;"> Long gamma-ray bursts (GRBs) are believed to originate from core collapse of massive stars. High-redshift GRBs can probe the star formation and reionization history of the early universe, but their detection remains rare. Here we report the detection of a GRB triggered in the 0.5--4 keV band by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated as EP240315a, whose bright peak was also detected by the Swift Burst Alert Telescope and Konus-Wind through off-line analyses. At a redshift of $z=4.859$, EP240315a showed a much longer and more complicated light curve in the soft X-ray band than in gamma-rays. Benefiting from a large field-of-view ($\sim$3600 deg$^2$) and a high sensitivity, EP-WXT captured the earlier engine activation and extended late engine activity through a continuous detection. With a peak X-ray flux at the faint end of previously known high-$z$ GRBs, the detection of EP240315a demonstrates the great potential for EP to study the early universe via GRBs. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2404.16425v1-abstract-full').style.display = 'none'; document.getElementById('2404.16425v1-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 April, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2024. </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">41 pages, 8 figures, 7 tables</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2308.12498">arXiv:2308.12498</a> <span> [<a href="https://arxiv.org/pdf/2308.12498">pdf</a>, <a href="https://arxiv.org/format/2308.12498">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"> Quiet, but not silent: Uncovering quiescent state properties of two transient High Mass X-ray binaries </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Raman%2C+G">Gayathri Raman</a>, <a href="/search/astro-ph?searchtype=author&query=Varun"> Varun</a>, <a href="/search/astro-ph?searchtype=author&query=Pradhan%2C+P">Pragati Pradhan</a>, <a href="/search/astro-ph?searchtype=author&query=Kennea%2C+J">Jamie Kennea</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="2308.12498v1-abstract-short" style="display: inline;"> We present the first set of broadband spectral and timing studies of two transient X-ray pulsars, MXB 0656-072 and MAXI J1409-619 using NuSTAR observations conducted during quiescence. Despite being captured at one of their lowest luminosity states, both these targets show signs of ongoing low-level accretion. Results from the time-averaged spectral analysis indicate for the first time, the presen… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2308.12498v1-abstract-full').style.display = 'inline'; document.getElementById('2308.12498v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2308.12498v1-abstract-full" style="display: none;"> We present the first set of broadband spectral and timing studies of two transient X-ray pulsars, MXB 0656-072 and MAXI J1409-619 using NuSTAR observations conducted during quiescence. Despite being captured at one of their lowest luminosity states, both these targets show signs of ongoing low-level accretion. Results from the time-averaged spectral analysis indicate for the first time, the presence of a strong soft power law component along with thermal emission from the neutron star hot spots. For both targets, the quiescent thermal X-ray emission is consistent with the deep crustal heating model. In MXB 0656-072, we do not detect any pulsations or indications of a cyclotron line during quiescence. However, in MAXI J1409-619 we detect strong pulsations at 502 s with a pulsed fraction of $\sim$66%, which adds this pulsar to the list of a handful of quiescent-state pulsating systems. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2308.12498v1-abstract-full').style.display = 'none'; document.getElementById('2308.12498v1-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 August, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2023. </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 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/2306.01454">arXiv:2306.01454</a> <span> [<a href="https://arxiv.org/pdf/2306.01454">pdf</a>, <a href="https://arxiv.org/format/2306.01454">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"> NuSTAR investigation of X-ray variability and hard X-ray spectral properties in IGR J16320-4751 and IGR J16479-4514 </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Varun"> Varun</a>, <a href="/search/astro-ph?searchtype=author&query=Raman%2C+G">Gayathri Raman</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="2306.01454v1-abstract-short" style="display: inline;"> We present the results obtained from a comprehensive timing and spectral study of two high-mass X-ray binary sources using NuSTAR observations. These two sources, IGR J16320-4751 and IGR J16479-4514, were discovered by INTEGRAL and have been characterized for the first time in the hard X-ray band (beyond 10~keV) in this work. In these sources, we observe the occurrence of intense X-ray flares, wit… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2306.01454v1-abstract-full').style.display = 'inline'; document.getElementById('2306.01454v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2306.01454v1-abstract-full" style="display: none;"> We present the results obtained from a comprehensive timing and spectral study of two high-mass X-ray binary sources using NuSTAR observations. These two sources, IGR J16320-4751 and IGR J16479-4514, were discovered by INTEGRAL and have been characterized for the first time in the hard X-ray band (beyond 10~keV) in this work. In these sources, we observe the occurrence of intense X-ray flares, with average luminosities exceeding 10$^{36}$~erg~s$^{-1}$. Our analysis reveals that these flares can be described consistently in the quasi-spherical accretion regime. The orbital phase of the first flare in NuSTAR observation of IGR J16479-4514 matches with the orbital phases of previous flares ($蠁=0.35$) in this source detected by other telescopes. We conclude that this flare occurs as a result of the periastron passage of the neutron star, rather than due to the presence of a corotating interaction region (CIR). Furthermore, from the energy-resolved pulse profile analysis of IGR J16320-4751, we find that the pulse fraction is lower in hard X-rays compared to soft X-rays. We present the hard X-ray spectral parameters of these two sources using several standard spectral model components. We do not detect a cyclotron absorption feature in either target. We provide estimates of the surface magnetic field strength of NS in IGR J16320-4751 using two indirect methods. Lastly, we observe spectral hardening during flaring segments compared to the off-flaring segments which indicates that comptonization is more effective during the flaring segments. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2306.01454v1-abstract-full').style.display = 'none'; document.getElementById('2306.01454v1-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 June, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> June 2023. </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, 6 figures, 7 tables. Accepted for publication 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/2210.02389">arXiv:2210.02389</a> <span> [<a href="https://arxiv.org/pdf/2210.02389">pdf</a>, <a href="https://arxiv.org/format/2210.02389">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/stac2901">10.1093/mnras/stac2901 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Timing and spectral studies of Cen X-3 in multiple luminosity states using $\textit{AstroSat}$ </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Bachhar%2C+R">Ritesh Bachhar</a>, <a href="/search/astro-ph?searchtype=author&query=Raman%2C+G">Gayathri Raman</a>, <a href="/search/astro-ph?searchtype=author&query=Bhalerao%2C+V">Varun Bhalerao</a>, <a href="/search/astro-ph?searchtype=author&query=Bhattacharya%2C+D">Dipankar Bhattacharya</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="2210.02389v1-abstract-short" style="display: inline;"> We present the results of timing and spectral analysis of the HMXB pulsar, Cen X-3, with the help of observations carried out using the Large Area X-ray Proportional Counter (LAXPC) on board $\textit{AstroSat}$. As part of our analysis, we sampled the source properties during 4 different observation epochs covering two widely different intensity states. We obtain a timing solution and report preci… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2210.02389v1-abstract-full').style.display = 'inline'; document.getElementById('2210.02389v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2210.02389v1-abstract-full" style="display: none;"> We present the results of timing and spectral analysis of the HMXB pulsar, Cen X-3, with the help of observations carried out using the Large Area X-ray Proportional Counter (LAXPC) on board $\textit{AstroSat}$. As part of our analysis, we sampled the source properties during 4 different observation epochs covering two widely different intensity states. We obtain a timing solution and report precise measurements of the spin and orbital parameters corresponding to these observational epochs. The pulse profiles during the two intensity states reveal dramatically varying shapes within a time span of one month. We report the detection of one of the lowest measured frequencies of quasi-periodic oscillations (QPO) at 0.026$\pm$0.001 Hz for Cen X-3 during its low-intensity state. We also find correlated periodic and aperiodic noise components in the power density spectra. We further carried out a phase averaged and a pulse phase resolved spectral study, where we find that the best fit continuum spectrum is well described by an absorbed comptonization model along with a blackbody. Cen X-3 exhibited the presence of the $\sim$28 keV CRSF absorption line and a $\sim$6.6 keV Fe emission line in both the intensity states. Significant variations in the line forming regions and mode of accretion for Cen X-3 within time spans of a month make Cen X-3 a highly dynamic persistent binary. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2210.02389v1-abstract-full').style.display = 'none'; document.getElementById('2210.02389v1-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 October, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> October 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, 8 figures, 2 tables</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2109.14022">arXiv:2109.14022</a> <span> [<a href="https://arxiv.org/pdf/2109.14022">pdf</a>, <a href="https://arxiv.org/format/2109.14022">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/stab2835">10.1093/mnras/stab2835 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> AstroSat detection of a mHz QPO and cyclotron line in IGR J19294+1816 during the 2019 outburst </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Raman%2C+G">Gayathri Raman</a>, <a href="/search/astro-ph?searchtype=author&query=Varun"> Varun</a>, <a href="/search/astro-ph?searchtype=author&query=Paul%2C+B">Biswajit Paul</a>, <a href="/search/astro-ph?searchtype=author&query=Bhattacharya%2C+D">Dipankar Bhattacharya</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="2109.14022v1-abstract-short" style="display: inline;"> We present results from timing and spectral analysis of the HMXB X-ray pulsar IGR J19294+1816 observed using \asr during its recent Type-I outburst in October, 2019. AstroSat observations sampled the outburst at the decline phase right after the outburst peak. We carried out timing analysis on the light curves obtained using the Large Area X-ray Proportional Counter (LAXPC) instrument on board Ast… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2109.14022v1-abstract-full').style.display = 'inline'; document.getElementById('2109.14022v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2109.14022v1-abstract-full" style="display: none;"> We present results from timing and spectral analysis of the HMXB X-ray pulsar IGR J19294+1816 observed using \asr during its recent Type-I outburst in October, 2019. AstroSat observations sampled the outburst at the decline phase right after the outburst peak. We carried out timing analysis on the light curves obtained using the Large Area X-ray Proportional Counter (LAXPC) instrument on board AstroSat and measured a spin period of 12.485065$\pm$0.000015 s. The peak in the power density spectrum (PDS) corresponding to the spin period of 12.48 s also shows a broadened base. We also detected a Quasi Periodic Oscillation (QPO) feature at 0.032$\pm$0.002 Hz with an RMS fractional amplitude of $\sim$18% in the PDS. We further carried out a joint spectral analysis using both the Soft X-ray Telescope (SXT) and the LAXPC instruments and detected a Cyclotron Resonant Scattering Feature (CRSF) at 42.7$\pm$0.9 keV and an Fe emission line at 6.4$\pm$0.1 keV. IGR J19294+1816, being an intermediate spin pulsar, has exhibited a plethora of spectral and timing features during its most recent 2019 outburst, adding it to the list of transients that exhibit both a QPO as well as a CRSF. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2109.14022v1-abstract-full').style.display = 'none'; document.getElementById('2109.14022v1-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 September, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2021. </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 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/2105.03937">arXiv:2105.03937</a> <span> [<a href="https://arxiv.org/pdf/2105.03937">pdf</a>, <a href="https://arxiv.org/ps/2105.03937">ps</a>, <a href="https://arxiv.org/format/2105.03937">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/stab2545">10.1093/mnras/stab2545 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> A comprehensive study of 2019-2020 flare of OJ 287 using AstroSat, Swift, and NuSTAR </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Prince%2C+R">Raj Prince</a>, <a href="/search/astro-ph?searchtype=author&query=Raman%2C+G">Gayathri Raman</a>, <a href="/search/astro-ph?searchtype=author&query=Khatoon%2C+R">Rukaiya Khatoon</a>, <a href="/search/astro-ph?searchtype=author&query=Agarwal%2C+A">Aditi Agarwal</a>, <a href="/search/astro-ph?searchtype=author&query=Varun"> Varun</a>, <a href="/search/astro-ph?searchtype=author&query=Gupta%2C+N">Nayantara Gupta</a>, <a href="/search/astro-ph?searchtype=author&query=Czerny%2C+B">Bo偶ena Czerny</a>, <a href="/search/astro-ph?searchtype=author&query=Majumdar%2C+P">Pratik Majumdar</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="2105.03937v3-abstract-short" style="display: inline;"> OJ 287 is a well-studied binary black hole system, that occasionally exhibits bright X-ray and optical flares. Here we present a detailed spectral study of its second brightest X-ray flare observed during 2019-2020 using archival Swift and NuSTAR observations along with ToO observations from AstroSat. The entire flaring period is divided into three states, defined as low, intermediate, and high st… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2105.03937v3-abstract-full').style.display = 'inline'; document.getElementById('2105.03937v3-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2105.03937v3-abstract-full" style="display: none;"> OJ 287 is a well-studied binary black hole system, that occasionally exhibits bright X-ray and optical flares. Here we present a detailed spectral study of its second brightest X-ray flare observed during 2019-2020 using archival Swift and NuSTAR observations along with ToO observations from AstroSat. The entire flaring period is divided into three states, defined as low, intermediate, and high states. The variation of hardness ratio (HR) with 0.3-10.0 keV integrated flux suggests a \enquote{softer-when-brighter} behavior, as also previously reported based on flux-index variations. Simultaneous high state X-ray spectra obtained using Swift, NuSTAR and AstroSat are very steep with a power-law index $>$2. A significant spectral change is observed in AstroSat-SXT and LAXPC spectrum which is consistent with Swift-XRT and NuSTAR spectrum. Together, optical-UV and X-ray spectrum during the high flux state, suggesting the emergence of a new high BL Lacertae (HBL) component. We have modeled the synchrotron peak with publicly available code named GAMERA for low, intermediate, and high flux state. Our modeling suggests the need of high magnetic field to explain the high state under the leptonic scenarios. Increase in the magnetic field value inside the jet could be linked to the increase in accretion rate as expected in the BH-disk impact scenario. The color-magnitude diagram reveals a \enquote{bluer-when-brighter} spectral energy distribution chromatism during the flaring period. Different chromatism or no chromatism at various occasions suggests a complex origin of optical emission, which is believed to be produced by disc impact or through synchrotron emission in the jet. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2105.03937v3-abstract-full').style.display = 'none'; document.getElementById('2105.03937v3-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 September, 2021; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 9 May, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2021. </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, 13 figures, 3 tables, Accepted 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/2008.07172">arXiv:2008.07172</a> <span> [<a href="https://arxiv.org/pdf/2008.07172">pdf</a>, <a href="https://arxiv.org/format/2008.07172">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/10.1016/j.newast.2020.101479">10.1016/j.newast.2020.101479 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Thermonuclear X-ray bursts detected in Cyg X-2 using AstroSat/LAXPC </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Devasia%2C+J">Jincy Devasia</a>, <a href="/search/astro-ph?searchtype=author&query=Raman%2C+G">Gayathri Raman</a>, <a href="/search/astro-ph?searchtype=author&query=Paul%2C+B">Biswajit Paul</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="2008.07172v1-abstract-short" style="display: inline;"> We report the detection of 5 Type-1 thermonuclear X-ray bursts and one burst-like event in the neutron star LMXB source, Cyg X-2 using X-ray data obtained with the Large Area X-ray Proportional Counter (LAXPC) instrument on board AstroSat. We carry out an energy resolved burst profile analysis as well as time resolved spectral analysis for each of the bursts and characterize their properties. All… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2008.07172v1-abstract-full').style.display = 'inline'; document.getElementById('2008.07172v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2008.07172v1-abstract-full" style="display: none;"> We report the detection of 5 Type-1 thermonuclear X-ray bursts and one burst-like event in the neutron star LMXB source, Cyg X-2 using X-ray data obtained with the Large Area X-ray Proportional Counter (LAXPC) instrument on board AstroSat. We carry out an energy resolved burst profile analysis as well as time resolved spectral analysis for each of the bursts and characterize their properties. All bursts are weak with burst peak-to-persistent intensity ratios $<$ 3, decay times $\sim$2 s, and with fluences $\sim$1$\times$10$^{-8}$ ergs/cm$^2$, indicating that the observed bursts are Helium fuelled flashes. An evolution of the blackbody temperature and radius is also observed during each burst. We carry out a search for Burst Oscillations (BO) and derive upper limits to the rms fractional amplitude for BO (for all the bursts) to be $\sim$1\%. We also carried out search for Quasi Periodic Oscillations (QPOs) in the power density spectra and we obtain upper limits to the fractional rms amplitude as $\sim$3.4\% at frequencies close to $\sim$5.6 Hz. We further carry out spectral and timing analysis of the non-burst persistent emission along with a study of the hardness-intensity and colour-colour diagrams. Using results from our analysis we infer that during this observation in 2016, Cyg X-2 can be characterized as being in the early Flaring Branch (FB) with a puffed up accretion disk and a clumpy coronal structure while undergoing medium-to-high levels of accretion. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2008.07172v1-abstract-full').style.display = 'none'; document.getElementById('2008.07172v1-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 August, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 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">Accepted for publication in New Astronomy</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1908.02168">arXiv:1908.02168</a> <span> [<a href="https://arxiv.org/pdf/1908.02168">pdf</a>, <a href="https://arxiv.org/format/1908.02168">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Solar and Stellar Astrophysics">astro-ph.SR</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</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/10.3847/2041-8213/ab543f">10.3847/2041-8213/ab543f <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Can Kilonova Light curves be Standardized? </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Kashyap%2C+R">Rahul Kashyap</a>, <a href="/search/astro-ph?searchtype=author&query=Raman%2C+G">Gayathri Raman</a>, <a href="/search/astro-ph?searchtype=author&query=Ajith%2C+P">Parameswaran Ajith</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="1908.02168v2-abstract-short" style="display: inline;"> Binary neutron star mergers have been recently confirmed to be the progenitors of the optical transients kilonovae (KNe). KNe are powered by the radioactive decay of neutron-rich elements (r-process elements) which are believed to be the product of disruption of neutron stars during their merger. KNe exhibit interesting parallels with type Ia supernovae (SNe), whose light curves show specific corr… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1908.02168v2-abstract-full').style.display = 'inline'; document.getElementById('1908.02168v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1908.02168v2-abstract-full" style="display: none;"> Binary neutron star mergers have been recently confirmed to be the progenitors of the optical transients kilonovae (KNe). KNe are powered by the radioactive decay of neutron-rich elements (r-process elements) which are believed to be the product of disruption of neutron stars during their merger. KNe exhibit interesting parallels with type Ia supernovae (SNe), whose light curves show specific correlations which allow them to be used as standardizable candles. In this paper, we investigate the possibility of the KN light curves exhibiting similar correlations. While a satisfactory answer to this question can only be provided by future KN observations, employing theoretical models we explore whether there is any ground for harboring such expectations. Using semi-analytic models of KN light curves in conjunction with results from numerical relativity simulations of binary neutron star mergers, we obtain the maximum bolometric luminosity ($L_{\mathrm{Bol}}^{\mathrm{max}}$) and decline in luminosity ($螖L_{\mathrm{Bol}}$) for a simulated population of mergers. We find that theoretical light curves of KNe show remarkable correlations despite the complex physics governing their behavior. This presents a possibility of future observations to uncover such correlations in the observed light curves, eventually allowing observers to standardize these light curves and to use them for local distance measurements. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1908.02168v2-abstract-full').style.display = 'none'; document.getElementById('1908.02168v2-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, 2020; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 6 August, 2019; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 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">3 pages; 3 figures; presented in GR22, Valencia</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> ApJL 886 L19 (2019) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1812.06108">arXiv:1812.06108</a> <span> [<a href="https://arxiv.org/pdf/1812.06108">pdf</a>, <a href="https://arxiv.org/ps/1812.06108">ps</a>, <a href="https://arxiv.org/format/1812.06108">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/sty3441">10.1093/mnras/sty3441 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Multitude of iron lines including a Compton scattered component in OAO 1657--415 detected with Chandra </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Pradhan%2C+P">Pragati Pradhan</a>, <a href="/search/astro-ph?searchtype=author&query=Raman%2C+G">Gayathri Raman</a>, <a href="/search/astro-ph?searchtype=author&query=Paul%2C+B">Biswajit Paul</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="1812.06108v1-abstract-short" style="display: inline;"> We present a high resolution X-ray spectrum of the accreting X-ray pulsar, OAO 1657--415 with HETG+ACIS-S onboard \emph{Chandra},revealing the presence of a broad line component around $\sim$ 6.3 keV associated with the neutral iron K$_伪$ line at 6.4 \rm{keV}. This is interpreted as Compton shoulder arising from the Compton scattering of the 6.4 \rm{keV} fluorescence photons making OAO 1657--415 t… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1812.06108v1-abstract-full').style.display = 'inline'; document.getElementById('1812.06108v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1812.06108v1-abstract-full" style="display: none;"> We present a high resolution X-ray spectrum of the accreting X-ray pulsar, OAO 1657--415 with HETG+ACIS-S onboard \emph{Chandra},revealing the presence of a broad line component around $\sim$ 6.3 keV associated with the neutral iron K$_伪$ line at 6.4 \rm{keV}. This is interpreted as Compton shoulder arising from the Compton scattering of the 6.4 \rm{keV} fluorescence photons making OAO 1657--415 the second accreting neutron star where such a feature is detected. A Compton shoulder reveals the presence of dense matter surrounding the X-ray source. We did not detect any periodicity in the lightcurve and obtained an upper limit of $\sim$ 2\% for the pulse fraction during this observation. This could be due to the smearing of the pulses when X-ray photons are scattered from a large region around the neutron star. In addition to the Fe K$_伪$, Fe $K_尾$ and Ni $K_伪$ lines already reported for this source, we also report for the first time, the presence of He-like and H-like iron emission lines at 6.7 and 6.97 \rm{keV} in the first order HETG spectrum. The detection of such ionized lines, indicative of a highly ionized surrounding medium, is rare in X-ray binaries. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1812.06108v1-abstract-full').style.display = 'none'; document.getElementById('1812.06108v1-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 December, 2018; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> December 2018. </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, 5 figures, accepted for publication 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/1808.05027">arXiv:1808.05027</a> <span> [<a href="https://arxiv.org/pdf/1808.05027">pdf</a>, <a href="https://arxiv.org/ps/1808.05027">ps</a>, <a href="https://arxiv.org/format/1808.05027">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/aadadb">10.3847/1538-4357/aadadb <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Fermi-Large Area Telescope observations of the brightest Gamma-ray flare ever detected from CTA 102 </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Prince%2C+R">Raj Prince</a>, <a href="/search/astro-ph?searchtype=author&query=Raman%2C+G">Gayathri Raman</a>, <a href="/search/astro-ph?searchtype=author&query=Hahn%2C+J">Joachim Hahn</a>, <a href="/search/astro-ph?searchtype=author&query=Gupta%2C+N">Nayantara Gupta</a>, <a href="/search/astro-ph?searchtype=author&query=Majumdar%2C+P">Pratik Majumdar</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="1808.05027v1-abstract-short" style="display: inline;"> We present a multi-wavelength study of the FSRQ CTA 102 using Fermi-LAT and simultaneous Swift-XRT/UVOT observations. The Fermi-LAT telescope detected one of the brightest flares from this object during Sep, 2016 to Mar, 2017. In the 190 days of observation period the source underwent four major flares. A detailed analysis of the temporal and spectral properties of these flares indicates the flare… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1808.05027v1-abstract-full').style.display = 'inline'; document.getElementById('1808.05027v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1808.05027v1-abstract-full" style="display: none;"> We present a multi-wavelength study of the FSRQ CTA 102 using Fermi-LAT and simultaneous Swift-XRT/UVOT observations. The Fermi-LAT telescope detected one of the brightest flares from this object during Sep, 2016 to Mar, 2017. In the 190 days of observation period the source underwent four major flares. A detailed analysis of the temporal and spectral properties of these flares indicates the flare at MJD 57751.594 has a $纬$-ray flux of (30.12$\pm$4.48)$\times 10^{-6}$ ph cm$^{-2}$ s$^{-1}$ (from 90 minutes binning) in the energy range of 0.1--300 GeV. This has been found to be the highest flux ever detected from CTA 102. Time dependent leptonic modelling of the pre-flare, rising state, flares and decaying state has been done. A single emission region of size $6.5\times 10^{16}$ cm has been used in our work to explain the multi-wavelength spectral energy distributions. During flares the luminosity in electrons increases nearly seventy times compared to the pre-flare state. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1808.05027v1-abstract-full').style.display = 'none'; document.getElementById('1808.05027v1-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> 15 August, 2018; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2018. </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, 7 figures, Accepted for Publication in 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/1804.06073">arXiv:1804.06073</a> <span> [<a href="https://arxiv.org/pdf/1804.06073">pdf</a>, <a href="https://arxiv.org/format/1804.06073">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/sty918">10.1093/mnras/sty918 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Observation of variable pre-eclipse dips and disk winds in the eclipsing LMXB XTE J1710-281 </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Raman%2C+G">Gayathri Raman</a>, <a href="/search/astro-ph?searchtype=author&query=Maitra%2C+C">Chandreyee Maitra</a>, <a href="/search/astro-ph?searchtype=author&query=Paul%2C+B">Biswajit Paul</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="1804.06073v1-abstract-short" style="display: inline;"> We report the first detection of highly ionized Fe species in the X-ray spectrum of the eclipsing and dipping Low Mass X-ray Binary XTE J1710-281. Using archival Chandra and Suzaku observations, we have carried out a spectro-timing analysis of the source during three different epochs. We compare the average orbital profile and obtain differences in pre-eclipse dip morphologies between different ob… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1804.06073v1-abstract-full').style.display = 'inline'; document.getElementById('1804.06073v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1804.06073v1-abstract-full" style="display: none;"> We report the first detection of highly ionized Fe species in the X-ray spectrum of the eclipsing and dipping Low Mass X-ray Binary XTE J1710-281. Using archival Chandra and Suzaku observations, we have carried out a spectro-timing analysis of the source during three different epochs. We compare the average orbital profile and obtain differences in pre-eclipse dip morphologies between different observation epochs. We observe an orbit to orbit evolution of the dips for the first time in this source in both the Chandra observations, reflecting changes in the structure of the accretion disc in timescales of hours. We further perform intensity resolved spectroscopy for both the Chandra and the Suzaku data to characterize the changes in the spectral parameters from the persistent to the dipping intervals. We find that the absorbers responsible for the dips, can be best described using a partially ionized partial covering absorber, with an ionization parameter, log($尉$) of $\sim$2. The photon index of the source remained at $\sim$2 during both the Chandra and the Suzaku observations. In the 0.6-9 keV Suzaku spectra, we detect a broad 0.72 keV Fe L-alpha emission line complex and two narrow absorption lines at $\sim$6.60 keV and $\sim$7.01 keV. The highly ionized Fe line signatures, being an indicator of accretion disc-winds, has been observed for the first time in XTE J1710-281. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1804.06073v1-abstract-full').style.display = 'none'; document.getElementById('1804.06073v1-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 April, 2018; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2018. </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 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/1702.03719">arXiv:1702.03719</a> <span> [<a href="https://arxiv.org/pdf/1702.03719">pdf</a>, <a href="https://arxiv.org/ps/1702.03719">ps</a>, <a href="https://arxiv.org/format/1702.03719">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/10.1016/j.newast.2017.02.001">10.1016/j.newast.2017.02.001 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> X-ray and optical orbital modulation of EXO 0748-676: A co-variability study using XMM-Newton </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Raman%2C+G">Gayathri Raman</a>, <a href="/search/astro-ph?searchtype=author&query=Paul%2C+B">Biswajit Paul</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="1702.03719v1-abstract-short" style="display: inline;"> We present a multi-wavelength timing study of the eclipsing low mass X-ray binary EXO 0748-676 (UY Vol) using XMM-Newton when the source was in a hard spectral state. The orbital optical and X-ray light curves show a fairly large amount of intensity modulation in the 7 observations taken during September-November, 2003, covering 36 complete binary orbits of EXO 0748-676. While assessing the non-bu… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1702.03719v1-abstract-full').style.display = 'inline'; document.getElementById('1702.03719v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1702.03719v1-abstract-full" style="display: none;"> We present a multi-wavelength timing study of the eclipsing low mass X-ray binary EXO 0748-676 (UY Vol) using XMM-Newton when the source was in a hard spectral state. The orbital optical and X-ray light curves show a fairly large amount of intensity modulation in the 7 observations taken during September-November, 2003, covering 36 complete binary orbits of EXO 0748-676. While assessing the non-burst variability, simultaneously in the optical and X-ray light curves, we find that they are not correlated at reprocessing or orbital time-scales, but are weakly correlated at a few 1000s of seconds time-scales. Although a large fraction of the optical emission is likely to be due to reprocessing, the lack of significant correlation and presence of large variability in the orbital X-ray and optical light curves is probably due to structures and structural changes in the accretion disk that produce, and sometimes mask the reprocessed signal in varying amounts. These disk structures could be induced, at least partly, by irradiation. From the observed modulations seen in the optical light curves, there is strong evidence of accretion disk evolution at time scales of a few hours. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1702.03719v1-abstract-full').style.display = 'none'; document.getElementById('1702.03719v1-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, 2017; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> February 2017. </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 New Astronomy</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1602.01607">arXiv:1602.01607</a> <span> [<a href="https://arxiv.org/pdf/1602.01607">pdf</a>, <a href="https://arxiv.org/ps/1602.01607">ps</a>, <a href="https://arxiv.org/format/1602.01607">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/stw290">10.1093/mnras/stw290 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> SALT observation of X-ray pulse reprocessing in 4U 1626-67 </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Raman%2C+G">Gayathri Raman</a>, <a href="/search/astro-ph?searchtype=author&query=Paul%2C+B">Biswajit Paul</a>, <a href="/search/astro-ph?searchtype=author&query=Bhattacharya%2C+D">Dipankar Bhattacharya</a>, <a href="/search/astro-ph?searchtype=author&query=Mohan%2C+V">Vijay Mohan</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="1602.01607v2-abstract-short" style="display: inline;"> We investigate optical reprocessing of X-rays in the LMXB pulsar 4U 1626-67 in its current spin-up phase using observations with Southern African Large Telescope (SALT), near-simultaneous observations with Swift-XRT and non-simultaneous RXTE-PCA observations and present the results of timing analysis. Using SALT observations carried out on 5th and 6th March, 2014, we detect some interesting reproc… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1602.01607v2-abstract-full').style.display = 'inline'; document.getElementById('1602.01607v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1602.01607v2-abstract-full" style="display: none;"> We investigate optical reprocessing of X-rays in the LMXB pulsar 4U 1626-67 in its current spin-up phase using observations with Southern African Large Telescope (SALT), near-simultaneous observations with Swift-XRT and non-simultaneous RXTE-PCA observations and present the results of timing analysis. Using SALT observations carried out on 5th and 6th March, 2014, we detect some interesting reprocessing signatures. We detect a weak optical Quasi Periodic Oscillation (QPO) in the power density spectrum on March 5th at 48 mHz with a fractional rms of 3.3% in spite of the fact that source shows no corresponding X-ray QPO in the spin-up phase. In the light curve obtained on March 5th, we detect a coherent pulsation at the spin period of ~7.677 s. A previously known, slightly down-shifted side-band is also detected at 129.92 mHz. The frequency spacing between main pulse and this side-band is different from earlier observations, though the statistical significance of the difference is limited. The light curve of 6th March displays short time-scale variability in the form of flares on timescales of a few minutes. Folded pulse profiles resulting from data of this night show an interesting trend of pulse peak drifting. This drift could be due to i) rapid changes in the reprocessing agent, like orbital motion of an accretion disk warp around the neutron star or ii) intrinsic pulse phase changes in X-rays. We also examine some X-ray light curves obtained with RXTE-PCA during 2008-2010 for pulse shape changes in short time scales during X-ray flares. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1602.01607v2-abstract-full').style.display = 'none'; document.getElementById('1602.01607v2-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 March, 2016; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 4 February, 2016; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> February 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">Accepted for publication in MNRAS</span> </p> </li> </ol> <div class="is-hidden-tablet">  <span class="help" style="display: inline-block;"><a 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