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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/2501.12190">arXiv:2501.12190</a> <span> [<a href="https://arxiv.org/pdf/2501.12190">pdf</a>, <a href="https://arxiv.org/format/2501.12190">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"> Modelling polarized X-ray pulses from accreting millisecond pulsars with X-PSI, using different surface patterns </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Salmi%2C+T">Tuomo Salmi</a>, <a href="/search/astro-ph?searchtype=author&query=Dorsman%2C+B">Bas Dorsman</a>, <a href="/search/astro-ph?searchtype=author&query=Watts%2C+A+L">Anna L. Watts</a>, <a href="/search/astro-ph?searchtype=author&query=Bobrikova%2C+A">Anna Bobrikova</a>, <a href="/search/astro-ph?searchtype=author&query=Di+Marco%2C+A">Alessandro Di Marco</a>, <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=Papitto%2C+A">Alessandro Papitto</a>, <a href="/search/astro-ph?searchtype=author&query=Pilia%2C+M">Maura Pilia</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Rankin%2C+J">John Rankin</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="2501.12190v1-abstract-short" style="display: inline;"> We present an analysis of polarized X-ray pulses based on simulated data for accreting millisecond pulsars (AMPs). We used the open-source X-ray Pulse Simulation and Inference code (previously applied to NICER observations), that we upgraded to allow polarization analysis. We predicted neutron star parameter constraints for the Imaging X-ray Polarimetry Explorer (IXPE) and found that strong limits… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2501.12190v1-abstract-full').style.display = 'inline'; document.getElementById('2501.12190v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2501.12190v1-abstract-full" style="display: none;"> We present an analysis of polarized X-ray pulses based on simulated data for accreting millisecond pulsars (AMPs). We used the open-source X-ray Pulse Simulation and Inference code (previously applied to NICER observations), that we upgraded to allow polarization analysis. We predicted neutron star parameter constraints for the Imaging X-ray Polarimetry Explorer (IXPE) and found that strong limits on the hot region geometries can be hard to obtain if the emitting hot region is large and the number of polarized photons relatively small. However, if the star is bright enough and the hot regions are small and located so that polarization degree is higher, the observer inclination and hotspot colatitude can be constrained to a precision of within a few degrees. We also found that the shape of the hot region, whether a circle or a ring, cannot be distinguished in our most optimistic scenario. Nevertheless, future X-ray polarization missions are expected to improve the constraints, and already the recent AMP polarization detections by IXPE should help to infer the neutron star mass and radius when combined with modelling of X-ray pulse data sets that do not contain polarization information. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2501.12190v1-abstract-full').style.display = 'none'; document.getElementById('2501.12190v1-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 January, 2025; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> January 2025. </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, 3 figures, 1 table, 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/2501.05511">arXiv:2501.05511</a> <span> [<a href="https://arxiv.org/pdf/2501.05511">pdf</a>, <a href="https://arxiv.org/format/2501.05511">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/10.3847/2041-8213/ada7f8">10.3847/2041-8213/ada7f8 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> X-ray Dips and Polarization Angle Swings in GX 13+1 </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Di+Marco%2C+A">Alessandro Di Marco</a>, <a href="/search/astro-ph?searchtype=author&query=La+Monaca%2C+F">Fabio La Monaca</a>, <a href="/search/astro-ph?searchtype=author&query=Bobrikova%2C+A">Anna Bobrikova</a>, <a href="/search/astro-ph?searchtype=author&query=Stella%2C+L">Luigi Stella</a>, <a href="/search/astro-ph?searchtype=author&query=Papitto%2C+A">Alessandro Papitto</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Baglio%2C+M+C">Maria Cristina Baglio</a>, <a href="/search/astro-ph?searchtype=author&query=Bachetti%2C+M">Matteo Bachetti</a>, <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=Pilia%2C+M">Maura Pilia</a>, <a href="/search/astro-ph?searchtype=author&query=Rogantini%2C+D">Daniele Rogantini</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="2501.05511v2-abstract-short" style="display: inline;"> We present the result from the April 2024 observation of the low-mass X-ray binary GX 13+1 with the Imaging X-ray Polarimetry Explorer (IXPE), together with NICER and Swift-XRT coordinated observations. Two light curve dips were observed; during them, the harder Comptonized spectral component was dominant and the polarization degree higher than in the softer, off-dip intervals. Through a joint ana… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2501.05511v2-abstract-full').style.display = 'inline'; document.getElementById('2501.05511v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2501.05511v2-abstract-full" style="display: none;"> We present the result from the April 2024 observation of the low-mass X-ray binary GX 13+1 with the Imaging X-ray Polarimetry Explorer (IXPE), together with NICER and Swift-XRT coordinated observations. Two light curve dips were observed; during them, the harder Comptonized spectral component was dominant and the polarization degree higher than in the softer, off-dip intervals. Through a joint analysis of the three IXPE observations, which also included the dip from the first observation, we demonstrate that the polarization properties varied in response to the intensity and spectral hardness changes associated with the dips. The polarization degree attained values up to ~4%. The polarization angle showed a swing of ~70掳 across the dip and off-dip states, comparable to the continuous rotation seen during the first IXPE observation. We discuss these results in the context of models for polarized emission from the accretion disk and the boundary/spreading layer on the neutron star surface. We also draw attention to the role that an extended accretion disk corona or disk wind can play in generating high polarization degrees and, possibly, swings of the polarization angle. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2501.05511v2-abstract-full').style.display = 'none'; document.getElementById('2501.05511v2-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 February, 2025; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 9 January, 2025; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> January 2025. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Alessandro Di Marco et al 2025 ApJL 979 L47 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2409.16023">arXiv:2409.16023</a> <span> [<a href="https://arxiv.org/pdf/2409.16023">pdf</a>, <a href="https://arxiv.org/format/2409.16023">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"> Polarized radiation coming from the spreading layer of the weakly magnetized neutron stars </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Bobrikova%2C+A">Anna Bobrikova</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</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="2409.16023v1-abstract-short" style="display: inline;"> Observations show that the X-ray emission of the accreting weakly magnetized neutron stars is polarized. Here, we develop a theoretical model, where we assume the emission of the accreting neutron star coming from the spreading layer, the extension of the boundary between the disk and the neutron star surface onto the surface. We then calculate the Stokes parameters of the emission accounting for… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2409.16023v1-abstract-full').style.display = 'inline'; document.getElementById('2409.16023v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2409.16023v1-abstract-full" style="display: none;"> Observations show that the X-ray emission of the accreting weakly magnetized neutron stars is polarized. Here, we develop a theoretical model, where we assume the emission of the accreting neutron star coming from the spreading layer, the extension of the boundary between the disk and the neutron star surface onto the surface. We then calculate the Stokes parameters of the emission accounting for relativistic aberration and gravitational light bending in the Schwarzschild metric. We show that regardless of the geometry, for the spreading layer, we cannot expect the polarization degree to be higher than 1.5%. Our results have implications with regard to the understanding of the X-ray polarization from weakly magnetized neutron stars observed with the Imaging X-ray Polarimetry Explorer and the future enhanced X-ray Timing and Polarimetry mission. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2409.16023v1-abstract-full').style.display = 'none'; document.getElementById('2409.16023v1-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 September, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 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">9 pages, 7 figures, submitted 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/2409.07908">arXiv:2409.07908</a> <span> [<a href="https://arxiv.org/pdf/2409.07908">pdf</a>, <a href="https://arxiv.org/format/2409.07908">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"> Parameter constraints for accreting millisecond pulsars with synthetic NICER data </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Dorsman%2C+B">Bas Dorsman</a>, <a href="/search/astro-ph?searchtype=author&query=Salmi%2C+T">Tuomo Salmi</a>, <a href="/search/astro-ph?searchtype=author&query=Watts%2C+A+L">Anna L. Watts</a>, <a href="/search/astro-ph?searchtype=author&query=Ng%2C+M">Mason Ng</a>, <a href="/search/astro-ph?searchtype=author&query=Kamath%2C+S">Satish Kamath</a>, <a href="/search/astro-ph?searchtype=author&query=Bobrikova%2C+A">Anna Bobrikova</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=Kini%2C+Y">Yves Kini</a>, <a href="/search/astro-ph?searchtype=author&query=Choudhury%2C+D">Devarshi Choudhury</a>, <a href="/search/astro-ph?searchtype=author&query=Vinciguerra%2C+S">Serena Vinciguerra</a>, <a href="/search/astro-ph?searchtype=author&query=Bogdanov%2C+S">Slavko Bogdanov</a>, <a href="/search/astro-ph?searchtype=author&query=Chakrabarty%2C+D">Deepto Chakrabarty</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="2409.07908v1-abstract-short" style="display: inline;"> Pulse profile modelling (PPM) is a technique for inferring mass, radius and hotspot properties of millisecond pulsars. PPM is now regularly used for analysis of rotation-powered millisecond pulsars (RMPs) with data from the Neutron Star Interior Composition ExploreR (NICER). Extending PPM to accreting millisecond pulsars (AMPs) is attractive, because they are a different source class featuring bri… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2409.07908v1-abstract-full').style.display = 'inline'; document.getElementById('2409.07908v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2409.07908v1-abstract-full" style="display: none;"> Pulse profile modelling (PPM) is a technique for inferring mass, radius and hotspot properties of millisecond pulsars. PPM is now regularly used for analysis of rotation-powered millisecond pulsars (RMPs) with data from the Neutron Star Interior Composition ExploreR (NICER). Extending PPM to accreting millisecond pulsars (AMPs) is attractive, because they are a different source class featuring bright X-ray radiation from hotspots powered by accretion. In this paper, we present a modification of one of the PPM codes, X-PSI, so that it can be used for AMPs. In particular, we implement a model of an accretion disc and atmosphere model appropriate for the hotspots of AMPs, and improve the overall computational efficiency. We then test parameter recovery with synthetic NICER data in two scenarios with reasonable parameters for AMPs. We find in the first scenario, where the hotspot is large, that we are able to tightly and accurately constrain all parameters including mass and radius. In the second scenario, which is a high inclination system with a smaller hotspot, we find degeneracy between a subset of model parameters and a slight bias in the inferred mass and radius. This analysis of synthetic data lays the ground work for future analysis of AMPs with NICER data. Such an analysis could be complemented by future (joint) analysis of polarization data from the Imaging X-ray Polarimetry Explorer (IXPE). <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2409.07908v1-abstract-full').style.display = 'none'; document.getElementById('2409.07908v1-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 September, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 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">14 pages, 5 figures, 3 tables. Paper 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/2408.00608">arXiv:2408.00608</a> <span> [<a href="https://arxiv.org/pdf/2408.00608">pdf</a>, <a href="https://arxiv.org/ps/2408.00608">ps</a>, <a href="https://arxiv.org/format/2408.00608">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/10.1051/0004-6361/202451775">10.1051/0004-6361/202451775 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Discovery of Polarized X-Ray Emission from the Accreting Millisecond Pulsar SRGA J144459.2-604207 </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Papitto%2C+A">Alessandro Papitto</a>, <a href="/search/astro-ph?searchtype=author&query=Di+Marco%2C+A">Alessandro Di Marco</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Salmi%2C+T">Tuomo Salmi</a>, <a href="/search/astro-ph?searchtype=author&query=Illiano%2C+G">Giulia Illiano</a>, <a href="/search/astro-ph?searchtype=author&query=La+Monaca%2C+F">Fabio La Monaca</a>, <a href="/search/astro-ph?searchtype=author&query=Ambrosino%2C+F">Filippo Ambrosino</a>, <a href="/search/astro-ph?searchtype=author&query=Bobrikova%2C+A">Anna Bobrikova</a>, <a href="/search/astro-ph?searchtype=author&query=Baglio%2C+M+C">Maria Cristina Baglio</a>, <a href="/search/astro-ph?searchtype=author&query=Ballocco%2C+C">Caterina Ballocco</a>, <a href="/search/astro-ph?searchtype=author&query=Burderi%2C+L">Luciano Burderi</a>, <a href="/search/astro-ph?searchtype=author&query=Campana%2C+S">Sergio Campana</a>, <a href="/search/astro-ph?searchtype=author&query=Zelati%2C+F+C">Francesco Coti Zelati</a>, <a href="/search/astro-ph?searchtype=author&query=Di+Salvo%2C+T">Tiziana Di Salvo</a>, <a href="/search/astro-ph?searchtype=author&query=La+Placa%2C+R">Riccardo La Placa</a>, <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=Long%2C+S">Sinan Long</a>, <a href="/search/astro-ph?searchtype=author&query=Malacaria%2C+C">Christian Malacaria</a>, <a href="/search/astro-ph?searchtype=author&query=Zanon%2C+A+M">Arianna Miraval Zanon</a>, <a href="/search/astro-ph?searchtype=author&query=Ng%2C+M">Mason Ng</a>, <a href="/search/astro-ph?searchtype=author&query=Pilia%2C+M">Maura Pilia</a>, <a href="/search/astro-ph?searchtype=author&query=Sanna%2C+A">Andrea Sanna</a>, <a href="/search/astro-ph?searchtype=author&query=Stella%2C+L">Luigi Stella</a>, <a href="/search/astro-ph?searchtype=author&query=Strohmayer%2C+T">Tod Strohmayer</a>, <a href="/search/astro-ph?searchtype=author&query=Zane%2C+S">Silvia 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="2408.00608v2-abstract-short" style="display: inline;"> We report on the discovery of polarized X-ray emission from an accreting millisecond pulsar. During a 10-day-long coverage of the February 2024 outburst of SRGA J144459.2-604207, the Imaging X-ray Polarimetry Explorer (IXPE) detected an average polarization degree of the 2-8 keV emission of 2.3% +/- 0.4% at an angle of 59掳 +/- 6掳 (East of North; uncertainties quoted at the 1$蟽$ confidence level).… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2408.00608v2-abstract-full').style.display = 'inline'; document.getElementById('2408.00608v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2408.00608v2-abstract-full" style="display: none;"> We report on the discovery of polarized X-ray emission from an accreting millisecond pulsar. During a 10-day-long coverage of the February 2024 outburst of SRGA J144459.2-604207, the Imaging X-ray Polarimetry Explorer (IXPE) detected an average polarization degree of the 2-8 keV emission of 2.3% +/- 0.4% at an angle of 59掳 +/- 6掳 (East of North; uncertainties quoted at the 1$蟽$ confidence level). The polarized signal shows a significant energy dependence with a degree of 4.0% +/- 0.5% between 3 and 6 keV and < 1.5% (90% c.l.) in the 2-3 keV range. We used NICER, XMM-Newton, and NuSTAR observations to obtain an accurate pulse timing solution and perform a phase-resolved polarimetric analysis of IXPE data. We did not detect any significant variability of the Stokes parameters Q and U with the spin and the orbital phases. We used the relativistic rotating vector model to show that a moderately fan-beam emission from two point-like spots at a small magnetic obliquity ($\simeq$ 10掳) is compatible with the observed pulse profile and polarization properties. IXPE also detected 52 type-I X-ray bursts, with a recurrence time $螖t_{rec}$ increasing from 2 to 8 h as a function of the observed count rate $C$ as as $螖t_{rec} \simeq C^{-0.8}$ We stacked the emission observed during all the bursts and obtained an upper limit on the polarization degree of 8.5% (90% c.l.). <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2408.00608v2-abstract-full').style.display = 'none'; document.getElementById('2408.00608v2-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 1 August, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 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">10 pages, 10 figures, accepted for publication by A&A</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> A&A 694, A37 (2025) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2407.02655">arXiv:2407.02655</a> <span> [<a href="https://arxiv.org/pdf/2407.02655">pdf</a>, <a href="https://arxiv.org/format/2407.02655">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="Solar and Stellar Astrophysics">astro-ph.SR</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/10.1051/0004-6361/202451356">10.1051/0004-6361/202451356 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Ultrasoft state of microquasar Cygnus X-3: X-ray polarimetry reveals the geometry of astronomical puzzle </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Veledina%2C+A">Alexandra Veledina</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Bocharova%2C+A">Anastasiia Bocharova</a>, <a href="/search/astro-ph?searchtype=author&query=Di+Marco%2C+A">Alessandro Di Marco</a>, <a href="/search/astro-ph?searchtype=author&query=Forsblom%2C+S+V">Sofia V. Forsblom</a>, <a href="/search/astro-ph?searchtype=author&query=La+Monaca%2C+F">Fabio La Monaca</a>, <a href="/search/astro-ph?searchtype=author&query=Podgorny%2C+J">Jakub Podgorny</a>, <a href="/search/astro-ph?searchtype=author&query=Tsygankov%2C+S+S">Sergey S. Tsygankov</a>, <a href="/search/astro-ph?searchtype=author&query=Zdziarski%2C+A+A">Andrzej A. Zdziarski</a>, <a href="/search/astro-ph?searchtype=author&query=Ahlberg%2C+V">Varpu Ahlberg</a>, <a href="/search/astro-ph?searchtype=author&query=Green%2C+D+A">David A. Green</a>, <a href="/search/astro-ph?searchtype=author&query=Muleri%2C+F">Fabio Muleri</a>, <a href="/search/astro-ph?searchtype=author&query=Rhodes%2C+L">Lauren Rhodes</a>, <a href="/search/astro-ph?searchtype=author&query=Bianchi%2C+S">Stefano Bianchi</a>, <a href="/search/astro-ph?searchtype=author&query=Costa%2C+E">Enrico Costa</a>, <a href="/search/astro-ph?searchtype=author&query=Dovciak%2C+M">Michal Dovciak</a>, <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=McCollough%2C+M">Michael McCollough</a>, <a href="/search/astro-ph?searchtype=author&query=Soffitta%2C+P">Paolo Soffitta</a>, <a href="/search/astro-ph?searchtype=author&query=Sunyaev%2C+R">Rashid Sunyaev</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="2407.02655v1-abstract-short" style="display: inline;"> Cygnus X-3 is an enigmatic X-ray binary, that is both an exceptional accreting system and a cornerstone for the population synthesis studies. Prominent X-ray and radio properties follow a well-defined pattern, yet the physical reasons for the state changes observed in this system are not known. Recently, the presence of an optically thick envelope around the central source in the hard state was re… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2407.02655v1-abstract-full').style.display = 'inline'; document.getElementById('2407.02655v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2407.02655v1-abstract-full" style="display: none;"> Cygnus X-3 is an enigmatic X-ray binary, that is both an exceptional accreting system and a cornerstone for the population synthesis studies. Prominent X-ray and radio properties follow a well-defined pattern, yet the physical reasons for the state changes observed in this system are not known. Recently, the presence of an optically thick envelope around the central source in the hard state was revealed using the X-ray polarization data obtained with Imaging X-ray Polarimetry Explorer (IXPE). In this work, we analyse IXPE data obtained in the ultrasoft (radio quenched) state of the source. The average polarization degree (PD) of $11.9\pm0.5\%$ at a polarization angle (PA) of $94^{\circ}\pm1^{\circ}$ is inconsistent with the simple geometry of the accretion disc viewed at an intermediate inclination. The high PD, the blackbody-like spectrum, and the weakness of fluorescent iron line imply that the central source is hidden behind the optically thick outflow and its beamed radiation is scattered towards our line of sight. In this picture the observed PD is directly related to the source inclination, which we conservatively determine to lie in the range $26^{\circ}<i<28^{\circ}$. Using the new polarimetric properties, we propose the scenario that can be responsible for the cyclic behaviour of the state changes in the binary. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2407.02655v1-abstract-full').style.display = 'none'; document.getElementById('2407.02655v1-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 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">9 pages, 11 figures, submitted to A&A</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> A&A 688, L27 (2024) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2406.12014">arXiv:2406.12014</a> <span> [<a href="https://arxiv.org/pdf/2406.12014">pdf</a>, <a href="https://arxiv.org/format/2406.12014">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"> An IXPE-Led X-ray Spectro-Polarimetric Campaign on the Soft State of Cygnus X-1: X-ray Polarimetric Evidence for Strong Gravitational Lensing </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Steiner%2C+J+F">James F. Steiner</a>, <a href="/search/astro-ph?searchtype=author&query=Nathan%2C+E">Edward Nathan</a>, <a href="/search/astro-ph?searchtype=author&query=Hu%2C+K">Kun Hu</a>, <a href="/search/astro-ph?searchtype=author&query=Krawczynski%2C+H">Henric Krawczynski</a>, <a href="/search/astro-ph?searchtype=author&query=Dovciak%2C+M">Michal Dovciak</a>, <a href="/search/astro-ph?searchtype=author&query=Veledina%2C+A">Alexandra Veledina</a>, <a href="/search/astro-ph?searchtype=author&query=Muleri%2C+F">Fabio Muleri</a>, <a href="/search/astro-ph?searchtype=author&query=Svoboda%2C+J">Jiri Svoboda</a>, <a href="/search/astro-ph?searchtype=author&query=Alabarta%2C+K">Kevin Alabarta</a>, <a href="/search/astro-ph?searchtype=author&query=Parra%2C+M">Maxime Parra</a>, <a href="/search/astro-ph?searchtype=author&query=Bhargava%2C+Y">Yash Bhargava</a>, <a href="/search/astro-ph?searchtype=author&query=Matt%2C+G">Giorgio Matt</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Petrucci%2C+P">Pierre-Olivier Petrucci</a>, <a href="/search/astro-ph?searchtype=author&query=Tennant%2C+A+F">Allyn F. Tennant</a>, <a href="/search/astro-ph?searchtype=author&query=Baglio%2C+M+C">M. Cristina Baglio</a>, <a href="/search/astro-ph?searchtype=author&query=Baldini%2C+L">Luca Baldini</a>, <a href="/search/astro-ph?searchtype=author&query=Barnier%2C+S">Samuel Barnier</a>, <a href="/search/astro-ph?searchtype=author&query=Bhattacharyya%2C+S">Sudip Bhattacharyya</a>, <a href="/search/astro-ph?searchtype=author&query=Bianchi%2C+S">Stefano Bianchi</a>, <a href="/search/astro-ph?searchtype=author&query=Brigitte%2C+M">Maimouna Brigitte</a>, <a href="/search/astro-ph?searchtype=author&query=Cabezas%2C+M">Mauricio Cabezas</a>, <a href="/search/astro-ph?searchtype=author&query=Cangemi%2C+F">Floriane Cangemi</a>, <a href="/search/astro-ph?searchtype=author&query=Capitanio%2C+F">Fiamma Capitanio</a>, <a href="/search/astro-ph?searchtype=author&query=Casey%2C+J">Jacob Casey</a> , et al. (112 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="2406.12014v1-abstract-short" style="display: inline;"> We present the first X-ray spectropolarimetric results for Cygnus X-1 in its soft state from a campaign of five IXPE observations conducted during 2023 May-June. Companion multiwavelength data during the campaign are likewise shown. The 2-8 keV X-rays exhibit a net polarization degree PD=1.99%+/-0.13% (68% confidence). The polarization signal is found to increase with energy across IXPE's 2-8 keV… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2406.12014v1-abstract-full').style.display = 'inline'; document.getElementById('2406.12014v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2406.12014v1-abstract-full" style="display: none;"> We present the first X-ray spectropolarimetric results for Cygnus X-1 in its soft state from a campaign of five IXPE observations conducted during 2023 May-June. Companion multiwavelength data during the campaign are likewise shown. The 2-8 keV X-rays exhibit a net polarization degree PD=1.99%+/-0.13% (68% confidence). The polarization signal is found to increase with energy across IXPE's 2-8 keV bandpass. The polarized X-rays exhibit an energy-independent polarization angle of PA=-25.7+/-1.8 deg. East of North (68% confidence). This is consistent with being aligned to Cyg X-1's AU-scale compact radio jet and its pc-scale radio lobes. In comparison to earlier hard-state observations, the soft state exhibits a factor of 2 lower polarization degree, but a similar trend with energy and a similar (also energy-independent) position angle. When scaling by the natural unit of the disk temperature, we find the appearance of a consistent trendline in the polarization degree between soft and hard states. Our favored polarimetric model indicates Cyg X-1's spin is likely high (a* above ~0.96). The substantial X-ray polarization in Cyg X-1's soft state is most readily explained as resulting from a large portion of X-rays emitted from the disk returning and reflecting off the disk surface, generating a high polarization degree and a polarization direction parallel to the black hole spin axis and radio jet. In IXPE's bandpass, the polarization signal is dominated by the returning reflection emission. This constitutes polarimetric evidence for strong gravitational lensing of X-rays close to the black hole. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2406.12014v1-abstract-full').style.display = 'none'; document.getElementById('2406.12014v1-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 June, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> June 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">20 pages, accepted for publication in ApJL</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2406.08988">arXiv:2406.08988</a> <span> [<a href="https://arxiv.org/pdf/2406.08988">pdf</a>, <a href="https://arxiv.org/format/2406.08988">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/10.1051/0004-6361/202450937">10.1051/0004-6361/202450937 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Probing the polarized emission from SMC X-1: the brightest X-ray pulsar observed by IXPE </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Forsblom%2C+S+V">Sofia V. Forsblom</a>, <a href="/search/astro-ph?searchtype=author&query=Tsygankov%2C+S+S">Sergey S. Tsygankov</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Doroshenko%2C+V">Victor Doroshenko</a>, <a href="/search/astro-ph?searchtype=author&query=Mushtukov%2C+A+A">Alexander A. Mushtukov</a>, <a href="/search/astro-ph?searchtype=author&query=Ng%2C+M">Mason Ng</a>, <a href="/search/astro-ph?searchtype=author&query=Ravi%2C+S">Swati Ravi</a>, <a href="/search/astro-ph?searchtype=author&query=Marshall%2C+H+L">Herman L. Marshall</a>, <a href="/search/astro-ph?searchtype=author&query=Di+Marco%2C+A">Alessandro Di Marco</a>, <a href="/search/astro-ph?searchtype=author&query=La+Monaca%2C+F">Fabio La Monaca</a>, <a href="/search/astro-ph?searchtype=author&query=Malacaria%2C+C">Christian Malacaria</a>, <a href="/search/astro-ph?searchtype=author&query=Mastroserio%2C+G">Guglielmo Mastroserio</a>, <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=Possenti%2C+A">Andrea Possenti</a>, <a href="/search/astro-ph?searchtype=author&query=Suleimanov%2C+V+F">Valery F. Suleimanov</a>, <a href="/search/astro-ph?searchtype=author&query=Taverna%2C+R">Roberto Taverna</a>, <a href="/search/astro-ph?searchtype=author&query=Agudo%2C+I">Ivan Agudo</a>, <a href="/search/astro-ph?searchtype=author&query=Antonelli%2C+L+A">Lucio A. Antonelli</a>, <a href="/search/astro-ph?searchtype=author&query=Bachetti%2C+M">Matteo Bachetti</a>, <a href="/search/astro-ph?searchtype=author&query=Baldini%2C+L">Luca Baldini</a>, <a href="/search/astro-ph?searchtype=author&query=Baumgartner%2C+W+H">Wayne H. Baumgartner</a>, <a href="/search/astro-ph?searchtype=author&query=Bellazzini%2C+R">Ronaldo Bellazzini</a>, <a href="/search/astro-ph?searchtype=author&query=Bianchi%2C+S">Stefano Bianchi</a>, <a href="/search/astro-ph?searchtype=author&query=Bongiorno%2C+S+D">Stephen D. Bongiorno</a>, <a href="/search/astro-ph?searchtype=author&query=Bonino%2C+R">Raffaella Bonino</a> , et al. (79 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="2406.08988v1-abstract-short" style="display: inline;"> Recent observations of X-ray pulsars (XRPs) performed by the Imaging X-ray Polarimetry Explorer (IXPE) have made it possible to investigate the intricate details of these objects in a new way, thanks to the added value of X-ray polarimetry. Here we present the results of the IXPE observations of SMC X-1, a member of the small group of XRPs displaying super-orbital variability. SMC X-1 was observed… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2406.08988v1-abstract-full').style.display = 'inline'; document.getElementById('2406.08988v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2406.08988v1-abstract-full" style="display: none;"> Recent observations of X-ray pulsars (XRPs) performed by the Imaging X-ray Polarimetry Explorer (IXPE) have made it possible to investigate the intricate details of these objects in a new way, thanks to the added value of X-ray polarimetry. Here we present the results of the IXPE observations of SMC X-1, a member of the small group of XRPs displaying super-orbital variability. SMC X-1 was observed by IXPE three separate times during the high state of its super-orbital period. The observed luminosity in the 2-8 keV energy band of $L=2\times10^{38}$ erg/s makes SMC X-1 the brightest XRP ever observed by IXPE. We detect significant polarization in all three observations, with values of the phase-averaged polarization degree (PD) and polarization angle (PA) of $3.2\pm0.8$% and $97掳\pm8掳$ for Observation 1, $3.0\pm0.9$% and $90掳\pm8掳$ for Observation 2, and $5.5\pm1.1$% and $80掳\pm6掳$ for Observation 3, for the spectro-polarimetric analysis. The observed PD shows an increase over time with decreasing luminosity, while the PA decreases in decrements of 10掳. The phase-resolved spectro-polarimetric analysis reveals significant detection of polarization in three out of seven phase bins, with the PD ranging between 2% and 10%, and a corresponding range in the PA from $\sim$70掳 to $\sim$100掳. The pulse-phase resolved PD displays an apparent anti-correlation with the flux. Using the rotating vector model, we obtain constraints on the pulsar's geometrical properties for the individual observations. The position angle of the pulsar displays an evolution over time supporting the idea that we observe changes related to different super-orbital phases. Scattering in the wind of the precessing accretion disk may be responsible for the behavior of the polarimetric properties observed during the high-state of SMC X-1's super-orbital period. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2406.08988v1-abstract-full').style.display = 'none'; document.getElementById('2406.08988v1-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 June, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> June 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">11 pages, 11 figures, submitted to A&A</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> A&A 691, A216 (2024) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2405.08107">arXiv:2405.08107</a> <span> [<a href="https://arxiv.org/pdf/2405.08107">pdf</a>, <a href="https://arxiv.org/format/2405.08107">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="Solar and Stellar Astrophysics">astro-ph.SR</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/10.1051/0004-6361/202450696">10.1051/0004-6361/202450696 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Studying geometry of the ultraluminous X-ray pulsar Swift J0243.6+6124 using X-ray and optical polarimetry </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Tsygankov%2C+S+S">Sergey S. Tsygankov</a>, <a href="/search/astro-ph?searchtype=author&query=Doroshenko%2C+V">Victor Doroshenko</a>, <a href="/search/astro-ph?searchtype=author&query=Forsblom%2C+S+V">Sofia V. Forsblom</a>, <a href="/search/astro-ph?searchtype=author&query=Jenke%2C+P">Peter Jenke</a>, <a href="/search/astro-ph?searchtype=author&query=Kaaret%2C+P">Philip Kaaret</a>, <a href="/search/astro-ph?searchtype=author&query=Berdyugin%2C+A+V">Andrei V. Berdyugin</a>, <a href="/search/astro-ph?searchtype=author&query=Blinov%2C+D">Dmitry Blinov</a>, <a href="/search/astro-ph?searchtype=author&query=Kravtsov%2C+V">Vadim Kravtsov</a>, <a href="/search/astro-ph?searchtype=author&query=Liodakis%2C+I">Ioannis Liodakis</a>, <a href="/search/astro-ph?searchtype=author&query=Tzouvanou%2C+A">Anastasia Tzouvanou</a>, <a href="/search/astro-ph?searchtype=author&query=Di+Marco%2C+A">Alessandro Di Marco</a>, <a href="/search/astro-ph?searchtype=author&query=Heyl%2C+J">Jeremy Heyl</a>, <a href="/search/astro-ph?searchtype=author&query=La+Monaca%2C+F">Fabio La Monaca</a>, <a href="/search/astro-ph?searchtype=author&query=Mushtukov%2C+A+A">Alexander A. Mushtukov</a>, <a href="/search/astro-ph?searchtype=author&query=Pavlov%2C+G+G">George G. Pavlov</a>, <a href="/search/astro-ph?searchtype=author&query=Salganik%2C+A">Alexander Salganik</a>, <a href="/search/astro-ph?searchtype=author&query=Veledina%2C+A">Alexandra Veledina</a>, <a href="/search/astro-ph?searchtype=author&query=Weisskopf%2C+M+C">Martin C. Weisskopf</a>, <a href="/search/astro-ph?searchtype=author&query=Zane%2C+S">Silvia Zane</a>, <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=Suleimanov%2C+V+F">Valery F. Suleimanov</a>, <a href="/search/astro-ph?searchtype=author&query=Wilson-Hodge%2C+C">Colleen Wilson-Hodge</a>, <a href="/search/astro-ph?searchtype=author&query=Berdyugina%2C+S+V">Svetlana V. Berdyugina</a>, <a href="/search/astro-ph?searchtype=author&query=Kagitani%2C+M">Masato Kagitani</a> , et al. (86 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="2405.08107v2-abstract-short" style="display: inline;"> Discovery of pulsations from a number of ULXs proved that accretion onto neutron stars can produce luminosities exceeding the Eddington limit by several orders of magnitude. The conditions necessary to achieve such high luminosities as well as the exact geometry of the accretion flow in the neutron star vicinity are, however, a matter of debate. The pulse phase-resolved polarization measurements t… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2405.08107v2-abstract-full').style.display = 'inline'; document.getElementById('2405.08107v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2405.08107v2-abstract-full" style="display: none;"> Discovery of pulsations from a number of ULXs proved that accretion onto neutron stars can produce luminosities exceeding the Eddington limit by several orders of magnitude. The conditions necessary to achieve such high luminosities as well as the exact geometry of the accretion flow in the neutron star vicinity are, however, a matter of debate. The pulse phase-resolved polarization measurements that became possible with the launch of the Imaging X-ray Polarimetry Explorer (IXPE) can be used to determine the pulsar geometry and its orientation relative to the orbital plane. They provide an avenue to test different theoretical models of ULX pulsars. In this paper we present the results of three IXPE observations of the first Galactic ULX pulsar Swift J0243.6+6124 during its 2023 outburst. We find strong variations in the polarization characteristics with the pulsar phase. The average polarization degree increases from about 5% to 15% as the flux dropped by a factor of three in the course of the outburst. The polarization angle (PA) as a function of the pulsar phase shows two peaks in the first two observations, but changes to a characteristic sawtooth pattern in the remaining data set. This is not consistent with a simple rotating vector model. Assuming the existence of an additional constant polarized component, we were able to fit the three observations with a common rotating vector model and obtain constraints on the pulsar geometry. In particular, we find the pulsar angular momentum inclination with respect to the line of sight of 15-40 deg, the magnetic obliquity of 60-80 deg, and the pulsar spin position angle of -50 deg, which significantly differs from the constant component PA of about 10 deg. Combining these X-ray measurements with the optical PA, we find evidence for at least a 30 deg misalignment between the pulsar angular momentum and the binary orbital axis. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2405.08107v2-abstract-full').style.display = 'none'; document.getElementById('2405.08107v2-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, 2024; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 13 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">13 pages, 10 figures, version published in A&A</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> A&A 691, A123 (2024) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2404.01859">arXiv:2404.01859</a> <span> [<a href="https://arxiv.org/pdf/2404.01859">pdf</a>, <a href="https://arxiv.org/format/2404.01859">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/10.1051/0004-6361/202450207">10.1051/0004-6361/202450207 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> New polarimetric study of the galactic X-ray burster GX 13+1 </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Bobrikova%2C+A">Anna Bobrikova</a>, <a href="/search/astro-ph?searchtype=author&query=Di+Marco%2C+A">Alessandro Di Marco</a>, <a href="/search/astro-ph?searchtype=author&query=La+Monaca%2C+F">Fabio La Monaca</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Forsblom%2C+S+V">Sofia V. Forsblom</a>, <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</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="2404.01859v2-abstract-short" style="display: inline;"> Weakly magnetized neutron stars (WMNS) are complicated sources with challenging phenomenology. For decades, they have been studied via spectrometry and timing. It has been established that the spectrum of WMNSs consists of several components traditionally associated with the accretion disk, the boundary or spreading layer, and the wind and their interactions with each other. Since 2022, WMNSs have… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2404.01859v2-abstract-full').style.display = 'inline'; document.getElementById('2404.01859v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2404.01859v2-abstract-full" style="display: none;"> Weakly magnetized neutron stars (WMNS) are complicated sources with challenging phenomenology. For decades, they have been studied via spectrometry and timing. It has been established that the spectrum of WMNSs consists of several components traditionally associated with the accretion disk, the boundary or spreading layer, and the wind and their interactions with each other. Since 2022, WMNSs have been actively observed with the Imaging X-ray Polarimetry Explorer (IXPE). Polarimetric studies provided new information about the behavior and geometry of these sources. One of the most enigmatic sources of the class, galactic X-ray burster GX 13+1 was first observed with IXPE in October 2023. A strongly variable polarization at the level 2-5$\%$ was detected with the source showing a rotation of the polarization angle (PA) that hinted towards the misalignment within the system. The second observation was performed in February 2024 with a complementary observation by Swift/XRT. IXPE measured an overall polarization degree (PD) of 2.5$\%$ and the PA of 24 degrees, and the Swift/XRT data helped us evaluate the galactic absorption and fit the continuum. Here we study the similarities and differences between the polarimetric properties of the source during the two observations. We confirm the expectation of the misalignment in the system and the assignment of the harder component to the boundary layer. We emphasize the importance of the wind in the system. We note the difference in the variation of polarimetric properties with energy and with time. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2404.01859v2-abstract-full').style.display = 'none'; document.getElementById('2404.01859v2-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, 2024; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 2 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">8 pages, 7 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> A&A 688, A217 (2024) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2401.13058">arXiv:2401.13058</a> <span> [<a href="https://arxiv.org/pdf/2401.13058">pdf</a>, <a href="https://arxiv.org/format/2401.13058">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/10.1051/0004-6361/202449318">10.1051/0004-6361/202449318 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Discovery of a strong rotation of the X-ray polarization angle in the galactic burster GX 13+1 </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Bobrikova%2C+A">Anna Bobrikova</a>, <a href="/search/astro-ph?searchtype=author&query=Forsblom%2C+S+V">Sofia V. Forsblom</a>, <a href="/search/astro-ph?searchtype=author&query=Di+Marco%2C+A">Alessandro Di Marco</a>, <a href="/search/astro-ph?searchtype=author&query=La+Monaca%2C+F">Fabio La Monaca</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Ng%2C+M">Mason Ng</a>, <a href="/search/astro-ph?searchtype=author&query=Ravi%2C+S">Swati Ravi</a>, <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=Kajava%2C+J+J+E">Jari J. E. Kajava</a>, <a href="/search/astro-ph?searchtype=author&query=Ursini%2C+F">Francesco Ursini</a>, <a href="/search/astro-ph?searchtype=author&query=Veledina%2C+A">Alexandra Veledina</a>, <a href="/search/astro-ph?searchtype=author&query=Rogantini%2C+D">Daniele Rogantini</a>, <a href="/search/astro-ph?searchtype=author&query=Salmi%2C+T">Tuomo Salmi</a>, <a href="/search/astro-ph?searchtype=author&query=Bianchi%2C+S">Stefano Bianchi</a>, <a href="/search/astro-ph?searchtype=author&query=Capitanio%2C+F">Fiamma Capitanio</a>, <a href="/search/astro-ph?searchtype=author&query=Done%2C+C">Chris Done</a>, <a href="/search/astro-ph?searchtype=author&query=Fabiani%2C+S">Sergio Fabiani</a>, <a href="/search/astro-ph?searchtype=author&query=Gnarini%2C+A">Andrea Gnarini</a>, <a href="/search/astro-ph?searchtype=author&query=Heyl%2C+J">Jeremy Heyl</a>, <a href="/search/astro-ph?searchtype=author&query=Kaaret%2C+P">Philip Kaaret</a>, <a href="/search/astro-ph?searchtype=author&query=Matt%2C+G">Giorgio Matt</a>, <a href="/search/astro-ph?searchtype=author&query=Muleri%2C+F">Fabio Muleri</a>, <a href="/search/astro-ph?searchtype=author&query=Nitindala%2C+A+P">Anagha P. Nitindala</a>, <a href="/search/astro-ph?searchtype=author&query=Rankin%2C+J">John Rankin</a>, <a href="/search/astro-ph?searchtype=author&query=Weisskopf%2C+M+C">Martin C. Weisskopf</a> , et al. (84 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="2401.13058v2-abstract-short" style="display: inline;"> Weakly magnetized neutron stars in X-ray binaries show complex phenomenology with several spectral components that can be associated with the accretion disk, boundary and/or spreading layer, a corona, and a wind. Spectroscopic information alone is, however, not enough to disentangle these components. Additional information about the nature of the spectral components and in particular the geometry… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2401.13058v2-abstract-full').style.display = 'inline'; document.getElementById('2401.13058v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2401.13058v2-abstract-full" style="display: none;"> Weakly magnetized neutron stars in X-ray binaries show complex phenomenology with several spectral components that can be associated with the accretion disk, boundary and/or spreading layer, a corona, and a wind. Spectroscopic information alone is, however, not enough to disentangle these components. Additional information about the nature of the spectral components and in particular the geometry of the emission region can be provided by X-ray polarimetry. One of the objects of the class, a bright, persistent, and rather peculiar galactic Type I X-ray burster was observed with the Imaging X-ray Polarimetry Explorer (IXPE) and the X-ray Multi-Mirror Mission Newton (XMM-Newton). Using the XMM-Newton data we estimated the current state of the source as well as detected strong absorption lines associated with the accretion disk wind. IXPE data showed the source to be significantly polarized in the 2-8 keV energy band with the overall polarization degree (PD) of 1.4% at a polarization angle (PA) of -2 degrees (errors at 68% confidence level). During the two-day long observation, we detected rotation of the PA by about 70 degrees with the corresponding changes in the PD from 2% to non-detectable and then up to 5%. These variations in polarization properties are not accompanied by visible changes in spectroscopic characteristics. The energy-resolved polarimetric analysis showed a significant change in polarization, from being strongly dependent on energy at the beginning of the observation to being almost constant with energy in the later parts of the observation. As a possible interpretation, we suggest the presence of a constant component of polarization, strong wind scattering, or different polarization of the two main spectral components with individually peculiar behavior. The rotation of the PA suggests a 30-degree misalignment of the neutron star spin from the orbital axis. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2401.13058v2-abstract-full').style.display = 'none'; document.getElementById('2401.13058v2-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 August, 2024; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 23 January, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> January 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">12 pages, 12 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> A&A 688, A170 (2024) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2311.05497">arXiv:2311.05497</a> <span> [<a href="https://arxiv.org/pdf/2311.05497">pdf</a>, <a href="https://arxiv.org/format/2311.05497">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"> Tracking the X-ray Polarization of the Black Hole Transient Swift J1727.8-1613 during a State Transition </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Ingram%2C+A">Adam Ingram</a>, <a href="/search/astro-ph?searchtype=author&query=Bollemeijer%2C+N">Niek Bollemeijer</a>, <a href="/search/astro-ph?searchtype=author&query=Veledina%2C+A">Alexandra Veledina</a>, <a href="/search/astro-ph?searchtype=author&query=Dovciak%2C+M">Michal Dovciak</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Egron%2C+E">Elise Egron</a>, <a href="/search/astro-ph?searchtype=author&query=Russell%2C+T+D">Thomas D. Russell</a>, <a href="/search/astro-ph?searchtype=author&query=Trushkin%2C+S+A">Sergei A. Trushkin</a>, <a href="/search/astro-ph?searchtype=author&query=Negro%2C+M">Michela Negro</a>, <a href="/search/astro-ph?searchtype=author&query=Ratheesh%2C+A">Ajay Ratheesh</a>, <a href="/search/astro-ph?searchtype=author&query=Capitanio%2C+F">Fiamma Capitanio</a>, <a href="/search/astro-ph?searchtype=author&query=Connors%2C+R">Riley Connors</a>, <a href="/search/astro-ph?searchtype=author&query=Neilsen%2C+J">Joseph Neilsen</a>, <a href="/search/astro-ph?searchtype=author&query=Kraus%2C+A">Alexander Kraus</a>, <a href="/search/astro-ph?searchtype=author&query=Iacolina%2C+M+N">Maria Noemi Iacolina</a>, <a href="/search/astro-ph?searchtype=author&query=Pellizzoni%2C+A">Alberto Pellizzoni</a>, <a href="/search/astro-ph?searchtype=author&query=Pilia%2C+M">Maura Pilia</a>, <a href="/search/astro-ph?searchtype=author&query=Carotenuto%2C+F">Francesco Carotenuto</a>, <a href="/search/astro-ph?searchtype=author&query=Matt%2C+G">Giorgio Matt</a>, <a href="/search/astro-ph?searchtype=author&query=Mastroserio%2C+G">Guglielmo Mastroserio</a>, <a href="/search/astro-ph?searchtype=author&query=Kaaret%2C+P">Philip Kaaret</a>, <a href="/search/astro-ph?searchtype=author&query=Bianchi%2C+S">Stefano Bianchi</a>, <a href="/search/astro-ph?searchtype=author&query=Garcia%2C+J+A">Javier A. Garcia</a>, <a href="/search/astro-ph?searchtype=author&query=Bachetti%2C+M">Matteo Bachetti</a>, <a href="/search/astro-ph?searchtype=author&query=Wu%2C+K">Kinwah Wu</a> , et al. (98 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="2311.05497v3-abstract-short" style="display: inline;"> We report on an observational campaign on the bright black hole X-ray binary Swift J1727.8$-$1613 centered around five observations by the Imaging X-ray Polarimetry Explorer (IXPE). These observations track for the first time the evolution of the X-ray polarization of a black hole X-ray binary across a hard to soft state transition. The 2--8 keV polarization degree decreased from $\sim$4\% to… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2311.05497v3-abstract-full').style.display = 'inline'; document.getElementById('2311.05497v3-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2311.05497v3-abstract-full" style="display: none;"> We report on an observational campaign on the bright black hole X-ray binary Swift J1727.8$-$1613 centered around five observations by the Imaging X-ray Polarimetry Explorer (IXPE). These observations track for the first time the evolution of the X-ray polarization of a black hole X-ray binary across a hard to soft state transition. The 2--8 keV polarization degree decreased from $\sim$4\% to $\sim$3\% across the five observations, but the polarization angle remained oriented in the North-South direction throughout. Based on observations with the Australia Telescope Compact Array (ATCA), we find that the intrinsic 7.25 GHz radio polarization aligns with the X-ray polarization. Assuming the radio polarization aligns with the jet direction (which can be tested in the future with higher spatial resolution images of the jet), our results imply that the X-ray corona is extended in the disk plane, rather than along the jet axis, for the entire hard intermediate state. This in turn implies that the long ($\gtrsim$10 ms) soft lags that we measure with the Neutron star Interior Composition ExploreR (NICER) are dominated by processes other than pure light-crossing delays. Moreover, we find that the evolution of the soft lag amplitude with spectral state does not follow the trend seen for other sources, implying that Swift J1727.8$-$1613 is a member of a hitherto under-sampled sub-population. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2311.05497v3-abstract-full').style.display = 'none'; document.getElementById('2311.05497v3-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 April, 2024; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 9 November, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> November 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 ApJ. 21 pages, 8 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/2309.02329">arXiv:2309.02329</a> <span> [<a href="https://arxiv.org/pdf/2309.02329">pdf</a>, <a href="https://arxiv.org/format/2309.02329">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/10.1051/0004-6361/202346833">10.1051/0004-6361/202346833 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Polarized radiation from an accretion shock in accreting millisecond pulsars using exact Compton scattering formalism </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Bobrikova%2C+A">Anna Bobrikova</a>, <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=Salmi%2C+T">Tuomo Salmi</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</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="2309.02329v1-abstract-short" style="display: inline;"> Pulse profiles of accreting millisecond pulsars can be used to determine neutron star (NS) parameters, such as their masses and radii, and therefore provide constraints on the equation of state of cold dense matter. Information obtained by the Imaging X-ray Polarimetry Explorer (IXPE) can be used to decipher pulsar inclination and magnetic obliquity, providing ever tighter constraints on other par… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2309.02329v1-abstract-full').style.display = 'inline'; document.getElementById('2309.02329v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2309.02329v1-abstract-full" style="display: none;"> Pulse profiles of accreting millisecond pulsars can be used to determine neutron star (NS) parameters, such as their masses and radii, and therefore provide constraints on the equation of state of cold dense matter. Information obtained by the Imaging X-ray Polarimetry Explorer (IXPE) can be used to decipher pulsar inclination and magnetic obliquity, providing ever tighter constraints on other parameters. In this paper, we develop a new emission model for accretion-powered millisecond pulsars based on thermal Comptonization in an accretion shock above the NS surface. The shock structure was approximated by an isothermal plane-parallel slab and the Stokes parameters of the emergent radiation were computed as a function of the zenith angle and energy for different values of the electron temperature, the Thomson optical depth of the slab, and the temperature of the seed blackbody photons. We show that our Compton scattering model leads to a significantly lower polarization degree of the emitted radiation compared to the previously used Thomson scattering model. We computed a large grid of shock models, which can be combined with pulse profile modeling techniques both with and without polarization included. In this work, we used the relativistic rotating vector model for the oblate NS in order to produce the observed Stokes parameters as a function of the pulsar phase. Furthermore, we simulated the data to be produced by IXPE and obtained constraints on model parameters using nested sampling. The developed methods can also be used in the analysis of the data from future satellites, such as the enhanced X-ray Timing and Polarimetry mission. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2309.02329v1-abstract-full').style.display = 'none'; document.getElementById('2309.02329v1-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 September, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 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 to A&A on 11 August 2023</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> A&A 678, A99 (2023) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2308.15159">arXiv:2308.15159</a> <span> [<a href="https://arxiv.org/pdf/2308.15159">pdf</a>, <a href="https://arxiv.org/format/2308.15159">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"> artpol: Analytical ray-tracing method for spectro-polarimetric properties of accretion disks around Kerr black holes </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=Veledina%2C+A">Alexandra Veledina</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=N%C3%A4ttil%C3%A4%2C+J">Joonas N盲ttil盲</a>, <a href="/search/astro-ph?searchtype=author&query=Suleimanov%2C+V+F">Valery F. Suleimanov</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="2308.15159v1-abstract-short" style="display: inline;"> Spectro-polarimetric signatures of accretion disks in X-ray binaries and active galactic nuclei contain information about the masses and spins of their central black holes, as well as the geometry of matter close to the compact objects. This information can be extracted using the means of X-ray polarimetry. In this work, we present a fast analytical ray-tracing technique for polarized light \texts… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2308.15159v1-abstract-full').style.display = 'inline'; document.getElementById('2308.15159v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2308.15159v1-abstract-full" style="display: none;"> Spectro-polarimetric signatures of accretion disks in X-ray binaries and active galactic nuclei contain information about the masses and spins of their central black holes, as well as the geometry of matter close to the compact objects. This information can be extracted using the means of X-ray polarimetry. In this work, we present a fast analytical ray-tracing technique for polarized light \textsc{artpol} that helps obtain the spinning black hole parameters from the observed properties. This technique can replace the otherwise time-consuming numerical ray-tracing calculations. We show that \textsc{artpol} proves accurate for Kerr black holes with dimensionless spin parameter $a\leq0.94$ while being over four orders of magnitude faster than direct ray-tracing calculations. This approach opens broad prospects for directly fitting the spectro-polarimetric data from the \textit{Imaging X-ray Polarimetry Explorer}. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2308.15159v1-abstract-full').style.display = 'none'; document.getElementById('2308.15159v1-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> 29 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">Submitted to Astronomy & Astrophysics</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2306.02116">arXiv:2306.02116</a> <span> [<a href="https://arxiv.org/pdf/2306.02116">pdf</a>, <a href="https://arxiv.org/format/2306.02116">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/10.1051/0004-6361/202347088">10.1051/0004-6361/202347088 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Complex variations of X-ray polarization in the X-ray pulsar LS V +44 17/RX J0440.9+4431 </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Doroshenko%2C+V">Victor Doroshenko</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Heyl%2C+J">Jeremy Heyl</a>, <a href="/search/astro-ph?searchtype=author&query=Tsygankov%2C+S+S">Sergey S. Tsygankov</a>, <a href="/search/astro-ph?searchtype=author&query=Caiazzo%2C+I">Ilaria Caiazzo</a>, <a href="/search/astro-ph?searchtype=author&query=Turolla%2C+R">Roberto Turolla</a>, <a href="/search/astro-ph?searchtype=author&query=Veledina%2C+A">Alexandra Veledina</a>, <a href="/search/astro-ph?searchtype=author&query=Weisskopf%2C+M+C">Martin C. Weisskopf</a>, <a href="/search/astro-ph?searchtype=author&query=Forsblom%2C+S+V">Sofia V. Forsblom</a>, <a href="/search/astro-ph?searchtype=author&query=Gonz%C3%A1lez-Caniulef%2C+D">Denis Gonz谩lez-Caniulef</a>, <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=Malacaria%2C+C">Christian Malacaria</a>, <a href="/search/astro-ph?searchtype=author&query=Mushtukov%2C+A+A">Alexander A. Mushtukov</a>, <a href="/search/astro-ph?searchtype=author&query=Suleimanov%2C+V+F">Valery F. Suleimanov</a>, <a href="/search/astro-ph?searchtype=author&query=Lutovinov%2C+A+A">Alexander A. Lutovinov</a>, <a href="/search/astro-ph?searchtype=author&query=Mereminskiy%2C+I+A">Ilya A. Mereminskiy</a>, <a href="/search/astro-ph?searchtype=author&query=Molkov%2C+S+V">Sergey V. Molkov</a>, <a href="/search/astro-ph?searchtype=author&query=Salganik%2C+A">Alexander Salganik</a>, <a href="/search/astro-ph?searchtype=author&query=Santangelo%2C+A">Andrea Santangelo</a>, <a href="/search/astro-ph?searchtype=author&query=Berdyugin%2C+A+V">Andrei V. Berdyugin</a>, <a href="/search/astro-ph?searchtype=author&query=Kravtsov%2C+V">Vadim Kravtsov</a>, <a href="/search/astro-ph?searchtype=author&query=Nitindala%2C+A+P">Anagha P. Nitindala</a>, <a href="/search/astro-ph?searchtype=author&query=Agudo%2C+I">Iv谩n Agudo</a>, <a href="/search/astro-ph?searchtype=author&query=Antonelli%2C+L+A">Lucio A. Antonelli</a>, <a href="/search/astro-ph?searchtype=author&query=Bachetti%2C+M">Matteo Bachetti</a> , et al. (87 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="2306.02116v2-abstract-short" style="display: inline;"> We report on Imaging X-ray polarimetry explorer (IXPE) observations of the Be-transient X-ray pulsar LS V +44 17/RX J0440.9+4431 made at two luminosity levels during the giant outburst in January--February 2023. Considering the observed spectral variability and changes in the pulse profiles, the source was likely caught in supercritical and subcritical states with significantly different emission-… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2306.02116v2-abstract-full').style.display = 'inline'; document.getElementById('2306.02116v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2306.02116v2-abstract-full" style="display: none;"> We report on Imaging X-ray polarimetry explorer (IXPE) observations of the Be-transient X-ray pulsar LS V +44 17/RX J0440.9+4431 made at two luminosity levels during the giant outburst in January--February 2023. Considering the observed spectral variability and changes in the pulse profiles, the source was likely caught in supercritical and subcritical states with significantly different emission-region geometry, associated with the presence of accretion columns and hot spots, respectively. We focus here on the pulse-phase-resolved polarimetric analysis and find that the observed dependencies of the polarization degree and polarization angle (PA) on the pulse phase are indeed drastically different for the two observations. The observed differences, if interpreted within the framework of the rotating vector model (RVM), imply dramatic variations in the spin axis inclination, the position angle, and the magnetic colatitude by tens of degrees within the space of just a few days. We suggest that the apparent changes in the observed PA phase dependence are predominantly related to the presence of an unpulsed polarized component in addition to the polarized radiation associated with the pulsar itself. We then show that the observed PA phase dependence in both observations can be explained with a single set of RVM parameters defining the pulsar's geometry. We also suggest that the additional polarized component is likely produced by scattering of the pulsar radiation in the equatorial disk wind. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2306.02116v2-abstract-full').style.display = 'none'; document.getElementById('2306.02116v2-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 August, 2023; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 3 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">10 pages, 7 figures, accepted in A&A</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> A&A 677, A57 (2023) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2305.13028">arXiv:2305.13028</a> <span> [<a href="https://arxiv.org/pdf/2305.13028">pdf</a>, <a href="https://arxiv.org/format/2305.13028">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"> The X-ray polarisation of the Seyfert 1 galaxy IC 4329A </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Ingram%2C+A">A. Ingram</a>, <a href="/search/astro-ph?searchtype=author&query=Ewing%2C+M">M. Ewing</a>, <a href="/search/astro-ph?searchtype=author&query=Marinucci%2C+A">A. Marinucci</a>, <a href="/search/astro-ph?searchtype=author&query=Tagliacozzo%2C+D">D. Tagliacozzo</a>, <a href="/search/astro-ph?searchtype=author&query=Rosario%2C+D+J">D. J. Rosario</a>, <a href="/search/astro-ph?searchtype=author&query=Veledina%2C+A">A. Veledina</a>, <a href="/search/astro-ph?searchtype=author&query=Kim%2C+D+E">D. E. Kim</a>, <a href="/search/astro-ph?searchtype=author&query=Marin%2C+F">F. Marin</a>, <a href="/search/astro-ph?searchtype=author&query=Bianchi%2C+S">S. Bianchi</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">J. Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Matt%2C+G">G. Matt</a>, <a href="/search/astro-ph?searchtype=author&query=Marshall%2C+H+L">H. L. Marshall</a>, <a href="/search/astro-ph?searchtype=author&query=Ursini%2C+F">F. Ursini</a>, <a href="/search/astro-ph?searchtype=author&query=De+Rosa%2C+A">A. De Rosa</a>, <a href="/search/astro-ph?searchtype=author&query=Petrucci%2C+P">P-O. Petrucci</a>, <a href="/search/astro-ph?searchtype=author&query=Madejski%2C+G">G. Madejski</a>, <a href="/search/astro-ph?searchtype=author&query=Barnouin%2C+T">T. Barnouin</a>, <a href="/search/astro-ph?searchtype=author&query=Di+Gesu%2C+L">L. Di Gesu</a>, <a href="/search/astro-ph?searchtype=author&query=Dovvciak%2C+M">M. Dovvciak</a>, <a href="/search/astro-ph?searchtype=author&query=Gianolli%2C+V+E">V. E. Gianolli</a>, <a href="/search/astro-ph?searchtype=author&query=Krawczynski%2C+H">H. Krawczynski</a>, <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">V. Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=Middei%2C+R">R. Middei</a>, <a href="/search/astro-ph?searchtype=author&query=Podgorny%2C+J">J. Podgorny</a>, <a href="/search/astro-ph?searchtype=author&query=Puccetti%2C+S">S. Puccetti</a> , et al. (83 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="2305.13028v2-abstract-short" style="display: inline;"> We present an X-ray spectro-polarimetric analysis of the bright Seyfert galaxy IC 4329A. The Imaging X-ray Polarimetry Explorer (IXPE) observed the source for ~500 ks, supported by XMM-Newton (~60 ks) and NuSTAR (~80 ks) exposures. We detect polarisation in the 2-8 keV band with 2.97 sigma confidence. We report a polarisation degree of $3.3\pm1.1$ per cent and a polarisation angle of $78\pm10$ deg… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2305.13028v2-abstract-full').style.display = 'inline'; document.getElementById('2305.13028v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2305.13028v2-abstract-full" style="display: none;"> We present an X-ray spectro-polarimetric analysis of the bright Seyfert galaxy IC 4329A. The Imaging X-ray Polarimetry Explorer (IXPE) observed the source for ~500 ks, supported by XMM-Newton (~60 ks) and NuSTAR (~80 ks) exposures. We detect polarisation in the 2-8 keV band with 2.97 sigma confidence. We report a polarisation degree of $3.3\pm1.1$ per cent and a polarisation angle of $78\pm10$ degrees (errors are 1 sigma confidence). The X-ray polarisation is consistent with being aligned with the radio jet, albeit partially due to large uncertainties on the radio position angle. We jointly fit the spectra from the three observatories to constrain the presence of a relativistic reflection component. From this, we obtain constraints on the inclination angle to the inner disc (< 39 degrees at 99 per cent confidence) and the disc inner radius (< 11 gravitational radii at 99 per cent confidence), although we note that modelling systematics in practice add to the quoted statistical error. Our spectro-polarimetric modelling indicates that the 2-8 keV polarisation is consistent with being dominated by emission directly observed from the X-ray corona, but the polarisation of the reflection component is completely unconstrained. Our constraints on viewer inclination and polarisation degree tentatively favour more asymmetric, possibly out-flowing, coronal geometries that produce more highly polarised emission, but the coronal geometry is unconstrained at the 3 sigma level. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2305.13028v2-abstract-full').style.display = 'none'; document.getElementById('2305.13028v2-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, 2023; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 22 May, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 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, 13 pages, 9 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/2304.12752">arXiv:2304.12752</a> <span> [<a href="https://arxiv.org/pdf/2304.12752">pdf</a>, <a href="https://arxiv.org/format/2304.12752">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/ad226e">10.3847/1538-4357/ad226e <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> X-ray Polarization of the Black Hole X-ray Binary 4U 1630-47 Challenges Standard Thin Accretion Disk Scenario </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Ratheesh%2C+A">Ajay Ratheesh</a>, <a href="/search/astro-ph?searchtype=author&query=Dov%C4%8Diak%2C+M">Michal Dov膷iak</a>, <a href="/search/astro-ph?searchtype=author&query=Krawczynski%2C+H">Henric Krawczynski</a>, <a href="/search/astro-ph?searchtype=author&query=Podgorn%C3%BD%2C+J">Jakub Podgorn媒</a>, <a href="/search/astro-ph?searchtype=author&query=Marra%2C+L">Lorenzo Marra</a>, <a href="/search/astro-ph?searchtype=author&query=Veledina%2C+A">Alexandra Veledina</a>, <a href="/search/astro-ph?searchtype=author&query=Suleimanov%2C+V">Valery Suleimanov</a>, <a href="/search/astro-ph?searchtype=author&query=Cavero%2C+N+R">Nicole Rodriguez Cavero</a>, <a href="/search/astro-ph?searchtype=author&query=Steiner%2C+J">James Steiner</a>, <a href="/search/astro-ph?searchtype=author&query=Svoboda%2C+J">Jiri Svoboda</a>, <a href="/search/astro-ph?searchtype=author&query=Marinucci%2C+A">Andrea Marinucci</a>, <a href="/search/astro-ph?searchtype=author&query=Bianchi%2C+S">Stefano Bianchi</a>, <a href="/search/astro-ph?searchtype=author&query=Negro%2C+M">Michela Negro</a>, <a href="/search/astro-ph?searchtype=author&query=Matt%2C+G">Giorgio Matt</a>, <a href="/search/astro-ph?searchtype=author&query=Tombesi%2C+F">Francesco Tombesi</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Ingram%2C+A">Adam Ingram</a>, <a href="/search/astro-ph?searchtype=author&query=Taverna%2C+R">Roberto Taverna</a>, <a href="/search/astro-ph?searchtype=author&query=West%2C+A">Andrew West</a>, <a href="/search/astro-ph?searchtype=author&query=Karas%2C+V">Vladimir Karas</a>, <a href="/search/astro-ph?searchtype=author&query=Ursini%2C+F">Francesco Ursini</a>, <a href="/search/astro-ph?searchtype=author&query=Soffitta%2C+P">Paolo Soffitta</a>, <a href="/search/astro-ph?searchtype=author&query=Capitanio%2C+F">Fiamma Capitanio</a>, <a href="/search/astro-ph?searchtype=author&query=Viscolo%2C+D">Domenico Viscolo</a>, <a href="/search/astro-ph?searchtype=author&query=Manfreda%2C+A">Alberto Manfreda</a> , et al. (90 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="2304.12752v2-abstract-short" style="display: inline;"> Large energy-dependent X-ray polarization degree is detected by the Imaging X-ray Polarimetry Explorer ({IXPE}) in the high-soft emission state of the black hole X-ray binary 4U 1630--47. The highly significant detection (at $\approx50蟽$ confidence level) of an unexpectedly high polarization, rising from $\sim6\%$ at $2$ keV to $\sim10\%$ at $8$ keV, cannot be easily reconciled with standard model… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2304.12752v2-abstract-full').style.display = 'inline'; document.getElementById('2304.12752v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2304.12752v2-abstract-full" style="display: none;"> Large energy-dependent X-ray polarization degree is detected by the Imaging X-ray Polarimetry Explorer ({IXPE}) in the high-soft emission state of the black hole X-ray binary 4U 1630--47. The highly significant detection (at $\approx50蟽$ confidence level) of an unexpectedly high polarization, rising from $\sim6\%$ at $2$ keV to $\sim10\%$ at $8$ keV, cannot be easily reconciled with standard models of thin accretion discs. In this work we compare the predictions of different theoretical models with the {IXPE} data and conclude that the observed polarization properties are compatible with a scenario in which matter accretes onto the black hole through a thin disc, covered by a partially-ionized atmosphere flowing away at mildly relativistic velocities. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2304.12752v2-abstract-full').style.display = 'none'; document.getElementById('2304.12752v2-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 March, 2024; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 25 April, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 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">Published in ApJ (https://doi.org/10.3847/1538-4357/ad226e)</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> 2024 ApJ 964 77 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2303.12541">arXiv:2303.12541</a> <span> [<a href="https://arxiv.org/pdf/2303.12541">pdf</a>, <a href="https://arxiv.org/format/2303.12541">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Astrophysics of Galaxies">astro-ph.GA</span> <span class="tag is-small is-grey 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/stad1697">10.1093/mnras/stad1697 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Uncovering the geometry of the hot X-ray corona in the Seyfert galaxy NGC4151 with IXPE </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Gianolli%2C+V+E">V. E. Gianolli</a>, <a href="/search/astro-ph?searchtype=author&query=Kim%2C+D+E">D. E. Kim</a>, <a href="/search/astro-ph?searchtype=author&query=Bianchi%2C+S">S. Bianchi</a>, <a href="/search/astro-ph?searchtype=author&query=Ag%C3%ADs-Gonz%C3%A1lez%2C+B">B. Ag铆s-Gonz谩lez</a>, <a href="/search/astro-ph?searchtype=author&query=Madejski%2C+G">G. Madejski</a>, <a href="/search/astro-ph?searchtype=author&query=Marin%2C+F">F. Marin</a>, <a href="/search/astro-ph?searchtype=author&query=Marinucci%2C+A">A. Marinucci</a>, <a href="/search/astro-ph?searchtype=author&query=Matt%2C+G">G. Matt</a>, <a href="/search/astro-ph?searchtype=author&query=Middei%2C+R">R. Middei</a>, <a href="/search/astro-ph?searchtype=author&query=Petrucci%2C+P">P-O. Petrucci</a>, <a href="/search/astro-ph?searchtype=author&query=Soffitta%2C+P">P. Soffitta</a>, <a href="/search/astro-ph?searchtype=author&query=Tagliacozzo%2C+D">D. Tagliacozzo</a>, <a href="/search/astro-ph?searchtype=author&query=Tombesi%2C+F">F. Tombesi</a>, <a href="/search/astro-ph?searchtype=author&query=Ursini%2C+F">F. Ursini</a>, <a href="/search/astro-ph?searchtype=author&query=Barnouin%2C+T">T. Barnouin</a>, <a href="/search/astro-ph?searchtype=author&query=De+Rosa%2C+A">A. De Rosa</a>, <a href="/search/astro-ph?searchtype=author&query=Di+Gesu%2C+L">L. Di Gesu</a>, <a href="/search/astro-ph?searchtype=author&query=Ingram%2C+A">A. Ingram</a>, <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">V. Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=Panagiotou%2C+C">C. Panagiotou</a>, <a href="/search/astro-ph?searchtype=author&query=Podgorny%2C+J">J. Podgorny</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">J. Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Puccetti%2C+S">S. Puccetti</a>, <a href="/search/astro-ph?searchtype=author&query=Ratheesh%2C+A">A. Ratheesh</a>, <a href="/search/astro-ph?searchtype=author&query=Veledina%2C+A">A. Veledina</a> , et al. (84 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="2303.12541v2-abstract-short" style="display: inline;"> We present an X-ray spectro-polarimetric analysis of the bright Seyfert galaxy NGC4151. The source has been observed with the Imaging X-ray Polarimetry Explorer (IXPE) for 700 ks, complemented with simultaneous XMM-Newton (50 ks) and NuSTAR (100 ks) pointings. A polarization degree $螤 = 4.9 {\pm} 1.1 \%$ and angle $唯= 86掳 {\pm} 7掳$ east of north ($68\%$ confidence level) are measured in the 2-8 ke… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2303.12541v2-abstract-full').style.display = 'inline'; document.getElementById('2303.12541v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2303.12541v2-abstract-full" style="display: none;"> We present an X-ray spectro-polarimetric analysis of the bright Seyfert galaxy NGC4151. The source has been observed with the Imaging X-ray Polarimetry Explorer (IXPE) for 700 ks, complemented with simultaneous XMM-Newton (50 ks) and NuSTAR (100 ks) pointings. A polarization degree $螤 = 4.9 {\pm} 1.1 \%$ and angle $唯= 86掳 {\pm} 7掳$ east of north ($68\%$ confidence level) are measured in the 2-8 keV energy range. The spectro-polarimetric analysis shows that the polarization could be entirely due to reflection. Given the low reflection flux in the IXPE band, this requires however a reflection with a very large ($> 38 \%$) polarization degree. Assuming more reasonable values, a polarization degree of the hot corona ranging from ${\sim}4$ to ${\sim}8\%$ is found. The observed polarization degree excludes a spherical lamppost geometry for the corona, suggesting instead a slab-like geometry, possibly a wedge, as determined via Monte Carlo simulations. This is further confirmed by the X-ray polarization angle, which coincides with the direction of the extended radio emission in this source, supposed to match the disc axis. NGC4151 is the first AGN with an X-ray polarization measure for the corona, illustrating the capabilities of X-ray polarimetry and IXPE in unveiling its geometry. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2303.12541v2-abstract-full').style.display = 'none'; document.getElementById('2303.12541v2-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 June, 2023; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 22 March, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 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">9 pages, 4 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/2303.01174">arXiv:2303.01174</a> <span> [<a href="https://arxiv.org/pdf/2303.01174">pdf</a>, <a href="https://arxiv.org/format/2303.01174">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="Solar and Stellar Astrophysics">astro-ph.SR</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/s41550-024-02294-9">10.1038/s41550-024-02294-9 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Cygnus X-3 revealed as a Galactic ultraluminous X-ray source by IXPE </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Veledina%2C+A">Alexandra Veledina</a>, <a href="/search/astro-ph?searchtype=author&query=Muleri%2C+F">Fabio Muleri</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Podgorn%C3%BD%2C+J">Jakub Podgorn媒</a>, <a href="/search/astro-ph?searchtype=author&query=Dov%C4%8Diak%2C+M">Michal Dov膷iak</a>, <a href="/search/astro-ph?searchtype=author&query=Capitanio%2C+F">Fiamma Capitanio</a>, <a href="/search/astro-ph?searchtype=author&query=Churazov%2C+E">Eugene Churazov</a>, <a href="/search/astro-ph?searchtype=author&query=De+Rosa%2C+A">Alessandra De Rosa</a>, <a href="/search/astro-ph?searchtype=author&query=Di+Marco%2C+A">Alessandro Di Marco</a>, <a href="/search/astro-ph?searchtype=author&query=Forsblom%2C+S">Sofia Forsblom</a>, <a href="/search/astro-ph?searchtype=author&query=Kaaret%2C+P">Philip Kaaret</a>, <a href="/search/astro-ph?searchtype=author&query=Krawczynski%2C+H">Henric Krawczynski</a>, <a href="/search/astro-ph?searchtype=author&query=La+Monaca%2C+F">Fabio La Monaca</a>, <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=Lutovinov%2C+A+A">Alexander A. Lutovinov</a>, <a href="/search/astro-ph?searchtype=author&query=Molkov%2C+S+V">Sergey V. Molkov</a>, <a href="/search/astro-ph?searchtype=author&query=Mushtukov%2C+A+A">Alexander A. Mushtukov</a>, <a href="/search/astro-ph?searchtype=author&query=Ratheesh%2C+A">Ajay Ratheesh</a>, <a href="/search/astro-ph?searchtype=author&query=Cavero%2C+N+R">Nicole Rodriguez Cavero</a>, <a href="/search/astro-ph?searchtype=author&query=Steiner%2C+J+F">James F. Steiner</a>, <a href="/search/astro-ph?searchtype=author&query=Sunyaev%2C+R+A">Rashid A. Sunyaev</a>, <a href="/search/astro-ph?searchtype=author&query=Tsygankov%2C+S+S">Sergey S. Tsygankov</a>, <a href="/search/astro-ph?searchtype=author&query=Zdziarski%2C+A+A">Andrzej A. Zdziarski</a>, <a href="/search/astro-ph?searchtype=author&query=Bianchi%2C+S">Stefano Bianchi</a>, <a href="/search/astro-ph?searchtype=author&query=Bright%2C+J+S">Joe S. Bright</a> , et al. (105 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="2303.01174v2-abstract-short" style="display: inline;"> The accretion of matter by compact objects can be inhibited by radiation pressure if the luminosity exceeds the critical value, known as the Eddington limit. Discovery of ultraluminous X-ray sources has shown that accretion can proceed even when the apparent luminosity significantly exceeds this limit. High apparent luminosity might be produced thanks to geometric beaming of the radiation by an ou… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2303.01174v2-abstract-full').style.display = 'inline'; document.getElementById('2303.01174v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2303.01174v2-abstract-full" style="display: none;"> The accretion of matter by compact objects can be inhibited by radiation pressure if the luminosity exceeds the critical value, known as the Eddington limit. Discovery of ultraluminous X-ray sources has shown that accretion can proceed even when the apparent luminosity significantly exceeds this limit. High apparent luminosity might be produced thanks to geometric beaming of the radiation by an outflow. The outflow half-opening angle, which determines the amplification due to beaming, has never been robustly constrained. Using the Imaging X-ray Polarimetry Explorer, we made the measurement of X-ray polarization in the Galactic X-ray binary Cyg X-3. We find high, over 20%, nearly energy-independent linear polarization, orthogonal to the direction of the radio ejections. These properties unambiguously indicate the presence of a collimating outflow in the X-ray binary Cyg~X-3 and constrain its half-opening angle, <15 degrees. Thus, the source can be used as a laboratory for studying the super-critical accretion regime. This finding underscores the importance of X-ray polarimetry in advancing our understanding of accreting sources. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2303.01174v2-abstract-full').style.display = 'none'; document.getElementById('2303.01174v2-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 August, 2024; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 2 March, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 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">52 pages, 14 figures, 3 tables. Author version of the article published in Nature 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/2212.09778">arXiv:2212.09778</a> <span> [<a href="https://arxiv.org/pdf/2212.09778">pdf</a>, <a href="https://arxiv.org/format/2212.09778">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/10.3847/2041-8213/acad81">10.3847/2041-8213/acad81 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Timing analysis of the 2022 outburst of the accreting millisecond X-ray pulsar SAX J1808.4$-$3658: hints of an orbital shrinking </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Illiano%2C+G">Giulia Illiano</a>, <a href="/search/astro-ph?searchtype=author&query=Papitto%2C+A">Alessandro Papitto</a>, <a href="/search/astro-ph?searchtype=author&query=Sanna%2C+A">Andrea Sanna</a>, <a href="/search/astro-ph?searchtype=author&query=Bult%2C+P">Peter Bult</a>, <a href="/search/astro-ph?searchtype=author&query=Ambrosino%2C+F">Filippo Ambrosino</a>, <a href="/search/astro-ph?searchtype=author&query=Zanon%2C+A+M">Arianna Miraval Zanon</a>, <a href="/search/astro-ph?searchtype=author&query=Zelati%2C+F+C">Francesco Coti Zelati</a>, <a href="/search/astro-ph?searchtype=author&query=Stella%2C+L">Luigi Stella</a>, <a href="/search/astro-ph?searchtype=author&query=Altamirano%2C+D">Diego Altamirano</a>, <a href="/search/astro-ph?searchtype=author&query=Baglio%2C+M+C">Maria Cristina Baglio</a>, <a href="/search/astro-ph?searchtype=author&query=Bozzo%2C+E">Enrico Bozzo</a>, <a href="/search/astro-ph?searchtype=author&query=Burderi%2C+L">Luciano Burderi</a>, <a href="/search/astro-ph?searchtype=author&query=de+Martino%2C+D">Domitilla de Martino</a>, <a href="/search/astro-ph?searchtype=author&query=Di+Marco%2C+A">Alessandro Di Marco</a>, <a href="/search/astro-ph?searchtype=author&query=di+Salvo%2C+T">Tiziana di Salvo</a>, <a href="/search/astro-ph?searchtype=author&query=Ferrigno%2C+C">Carlo Ferrigno</a>, <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=Marino%2C+A">Alessio Marino</a>, <a href="/search/astro-ph?searchtype=author&query=Ng%2C+M">Mason Ng</a>, <a href="/search/astro-ph?searchtype=author&query=Pilia%2C+M">Maura Pilia</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Salmi%2C+T">Tuomo Salmi</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="2212.09778v2-abstract-short" style="display: inline;"> We present a pulse timing analysis of NICER observations of the accreting millisecond X-ray pulsar SAX J1808.4$-$3658 during the outburst that started on 2022 August 19. Similar to previous outbursts, after decaying from a peak luminosity of $\simeq 1\times10^{36} \, \mathrm{erg \, s^{-1}}$ in about a week, the pulsar entered in a $\sim 1$ month-long reflaring stage. Comparison of the average puls… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2212.09778v2-abstract-full').style.display = 'inline'; document.getElementById('2212.09778v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2212.09778v2-abstract-full" style="display: none;"> We present a pulse timing analysis of NICER observations of the accreting millisecond X-ray pulsar SAX J1808.4$-$3658 during the outburst that started on 2022 August 19. Similar to previous outbursts, after decaying from a peak luminosity of $\simeq 1\times10^{36} \, \mathrm{erg \, s^{-1}}$ in about a week, the pulsar entered in a $\sim 1$ month-long reflaring stage. Comparison of the average pulsar spin frequency during the outburst with those previously measured confirmed the long-term spin derivative of $\dot谓_{\textrm{SD}}=-(1.15\pm0.06)\times 10^{-15} \, \mathrm{Hz\,s^{-1}}$, compatible with the spin-down torque of a $\approx 10^{26} \, \mathrm{G \, cm^3}$ rotating magnetic dipole. For the first time in the last twenty years, the orbital phase evolution shows evidence for a decrease of the orbital period. The long-term behaviour of the orbit is dominated by a $\sim 11 \, \mathrm{s}$ modulation of the orbital phase epoch consistent with a $\sim 21 \, \mathrm{yr}$ period. We discuss the observed evolution in terms of a coupling between the orbit and variations in the mass quadrupole of the companion star. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2212.09778v2-abstract-full').style.display = 'none'; document.getElementById('2212.09778v2-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 December, 2022; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 19 December, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> December 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">11 pages, 3 figures, 1 table. Accepted for publication in ApJ Letters</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2206.09972">arXiv:2206.09972</a> <span> [<a href="https://arxiv.org/pdf/2206.09972">pdf</a>, <a href="https://arxiv.org/format/2206.09972">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 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.add5399">10.1126/science.add5399 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Polarized x-rays constrain the disk-jet geometry in the black hole x-ray binary Cygnus X-1 </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Krawczynski%2C+H">Henric Krawczynski</a>, <a href="/search/astro-ph?searchtype=author&query=Muleri%2C+F">Fabio Muleri</a>, <a href="/search/astro-ph?searchtype=author&query=Dov%C4%8Diak%2C+M">Michal Dov膷iak</a>, <a href="/search/astro-ph?searchtype=author&query=Veledina%2C+A">Alexandra Veledina</a>, <a href="/search/astro-ph?searchtype=author&query=Cavero%2C+N+R">Nicole Rodriguez Cavero</a>, <a href="/search/astro-ph?searchtype=author&query=Svoboda%2C+J">Jiri Svoboda</a>, <a href="/search/astro-ph?searchtype=author&query=Ingram%2C+A">Adam Ingram</a>, <a href="/search/astro-ph?searchtype=author&query=Matt%2C+G">Giorgio Matt</a>, <a href="/search/astro-ph?searchtype=author&query=Garcia%2C+J+A">Javier A. Garcia</a>, <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=Negro%2C+M">Michela Negro</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</a>, <a href="/search/astro-ph?searchtype=author&query=Kitaguchi%2C+T">Takao Kitaguchi</a>, <a href="/search/astro-ph?searchtype=author&query=Podgorn%C3%BD%2C+J">Jakub Podgorn媒</a>, <a href="/search/astro-ph?searchtype=author&query=Rankin%2C+J">John Rankin</a>, <a href="/search/astro-ph?searchtype=author&query=Zhang%2C+W">Wenda Zhang</a>, <a href="/search/astro-ph?searchtype=author&query=Berdyugin%2C+A">Andrei Berdyugin</a>, <a href="/search/astro-ph?searchtype=author&query=Berdyugina%2C+S+V">Svetlana V. Berdyugina</a>, <a href="/search/astro-ph?searchtype=author&query=Bianchi%2C+S">Stefano Bianchi</a>, <a href="/search/astro-ph?searchtype=author&query=Blinov%2C+D">Dmitry Blinov</a>, <a href="/search/astro-ph?searchtype=author&query=Capitanio%2C+F">Fiamma Capitanio</a>, <a href="/search/astro-ph?searchtype=author&query=Di+Lalla%2C+N">Niccol貌 Di Lalla</a>, <a href="/search/astro-ph?searchtype=author&query=Draghis%2C+P">Paul Draghis</a>, <a href="/search/astro-ph?searchtype=author&query=Fabiani%2C+S">Sergio Fabiani</a>, <a href="/search/astro-ph?searchtype=author&query=Kagitani%2C+M">Masato Kagitani</a> , et al. (89 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="2206.09972v2-abstract-short" style="display: inline;"> A black hole x-ray binary (XRB) system forms when gas is stripped from a normal star and accretes onto a black hole, which heats the gas sufficiently to emit x-rays. We report a polarimetric observation of the XRB Cygnus X-1 using the Imaging x-ray Polarimetry Explorer. The electric field position angle aligns with the outflowing jet, indicating that the jet is launched from the inner x-ray emitti… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2206.09972v2-abstract-full').style.display = 'inline'; document.getElementById('2206.09972v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2206.09972v2-abstract-full" style="display: none;"> A black hole x-ray binary (XRB) system forms when gas is stripped from a normal star and accretes onto a black hole, which heats the gas sufficiently to emit x-rays. We report a polarimetric observation of the XRB Cygnus X-1 using the Imaging x-ray Polarimetry Explorer. The electric field position angle aligns with the outflowing jet, indicating that the jet is launched from the inner x-ray emitting region. The polarization degree is (4.01+-0.20)% at 2 to 8 kiloelectronvolts, implying that the accretion disk is viewed closer to edge-on than the binary orbit. The observations reveal that hot x-ray emitting plasma is spatially extended in a plane perpendicular to the jet axis, not parallel to the jet. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2206.09972v2-abstract-full').style.display = 'none'; document.getElementById('2206.09972v2-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 January, 2023; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 20 June, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> June 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">51 pages, 15 figures, 5 tables</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Science, Volume 378, Issue 6620, pp. 650-654 (2022) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2109.04827">arXiv:2109.04827</a> <span> [<a href="https://arxiv.org/pdf/2109.04827">pdf</a>, <a href="https://arxiv.org/format/2109.04827">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/10.1051/0004-6361/202142360">10.1051/0004-6361/202142360 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Analytical techniques for polarimetric imaging of accretion flows in Schwarzschild metric </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=Veledina%2C+A">Alexandra Veledina</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</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="2109.04827v1-abstract-short" style="display: inline;"> Emission from an accretion disc around compact objects, such as neutron stars and black holes, is expected to be significantly polarized. The polarization can be used to put constraints on geometrical and physical parameters of the compact sources -- their radii, masses and spins -- as well as to determine the orbital parameters. The radiation escaping from the innermost parts of the disc is stron… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2109.04827v1-abstract-full').style.display = 'inline'; document.getElementById('2109.04827v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2109.04827v1-abstract-full" style="display: none;"> Emission from an accretion disc around compact objects, such as neutron stars and black holes, is expected to be significantly polarized. The polarization can be used to put constraints on geometrical and physical parameters of the compact sources -- their radii, masses and spins -- as well as to determine the orbital parameters. The radiation escaping from the innermost parts of the disc is strongly affected by the gravitational field of the compact object and relativistic velocities of the matter. The straightforward calculation of the observed polarization signatures involves computationally expensive ray-tracing technique. At the same time, having fast computational routines for direct data fitting becomes increasingly important in light of the currently observed images of the accretion flow around supermassive black hole in M87 by the Event Horizon Telescope, infrared polarization signatures coming from Sgr A*, as well as for the upcoming X-ray polarization measurements by the Imaging X-ray Polarimetry Explorer and enhanced X-ray Timing and Polarimetry mission. In this work, we obtain an exact analytical expression for the rotation angle of polarization plane in Schwarzschild metric accounting for the effects of light bending and relativistic aberration. We show that the calculation of the observed flux, polarization degree and polarization angle as a function of energy can be performed analytically with high accuracy using approximate light-bending formula, lifting the need for the pre-computed tabular models in fitting routines. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2109.04827v1-abstract-full').style.display = 'none'; document.getElementById('2109.04827v1-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 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">14 pages, 11 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> A&A 660, A25 (2022) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2009.09744">arXiv:2009.09744</a> <span> [<a href="https://arxiv.org/pdf/2009.09744">pdf</a>, <a href="https://arxiv.org/format/2009.09744">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/10.1051/0004-6361/202039470">10.1051/0004-6361/202039470 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Neutron star parameter constraints for accretion-powered millisecond pulsars from the simulated IXPE data </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Salmi%2C+T">Tuomo Salmi</a>, <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=Korsman%2C+K">Karri Korsman</a>, <a href="/search/astro-ph?searchtype=author&query=Baldini%2C+L">Luca Baldini</a>, <a href="/search/astro-ph?searchtype=author&query=Tsygankov%2C+S+S">Sergey S. Tsygankov</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</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="2009.09744v2-abstract-short" style="display: inline;"> We have simulated the X-ray polarization data that can be obtained with the Imaging X-ray Polarimetry Explorer, when observing accretion-powered millisecond pulsars. We estimated the necessary exposure times for SAX J1808.4$-$3658 in order to obtain different accuracies in the measured time-dependent Stokes profiles integrated over all energy channels. We found that the measured relative errors de… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2009.09744v2-abstract-full').style.display = 'inline'; document.getElementById('2009.09744v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2009.09744v2-abstract-full" style="display: none;"> We have simulated the X-ray polarization data that can be obtained with the Imaging X-ray Polarimetry Explorer, when observing accretion-powered millisecond pulsars. We estimated the necessary exposure times for SAX J1808.4$-$3658 in order to obtain different accuracies in the measured time-dependent Stokes profiles integrated over all energy channels. We found that the measured relative errors depend strongly on the relative configuration of the observer and the emitting hotspot. The improvement in the minimum relative error in Stokes $Q$ and $U$ parameters as a function of observing time $t$ scales as $1/\sqrt{t}$, and spans the range from 30-90% with 200 ks exposure time to 20-60% with 500 ks exposure time (in case of data binned in 19 phase bins). The simulated data were also used to predict how accurate measurements of the geometrical parameters of the neutron star can be made when modelling only $Q$ and $U$ parameters, but not the flux. We found that the observer inclination and the hotspot co-latitude could be determined with better than 10 deg accuracy for most of the cases we considered. These measurements can be used to further constrain neutron star mass and radius when combined with modelling of the X-ray pulse profile. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2009.09744v2-abstract-full').style.display = 'none'; document.getElementById('2009.09744v2-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, 2021; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 21 September, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 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">12 pages, 11 figures, published in A&A</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> A&A 646, A23 (2021) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2009.08852">arXiv:2009.08852</a> <span> [<a href="https://arxiv.org/pdf/2009.08852">pdf</a>, <a href="https://arxiv.org/format/2009.08852">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/10.1051/0004-6361/202039134">10.1051/0004-6361/202039134 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Oblate Schwarzschild approximation for polarized radiation from rapidly rotating neutron stars </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/astro-ph?searchtype=author&query=Loktev%2C+V">Vladislav Loktev</a>, <a href="/search/astro-ph?searchtype=author&query=Salmi%2C+T">Tuomo Salmi</a>, <a href="/search/astro-ph?searchtype=author&query=N%C3%A4ttil%C3%A4%2C+J">Joonas N盲ttil盲</a>, <a href="/search/astro-ph?searchtype=author&query=Poutanen%2C+J">Juri Poutanen</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="2009.08852v1-abstract-short" style="display: inline;"> We have developed a complete theory for the calculation of the observed Stokes parameters for radiation emitted from the surface of a rapidly rotating neutron star (NS) using the oblate Schwarzschild approximation. We accounted for the rotation of the polarization plane due to relativistic effects along the path from the stellar surface to the observer. The results were shown to agree with those o… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2009.08852v1-abstract-full').style.display = 'inline'; document.getElementById('2009.08852v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2009.08852v1-abstract-full" style="display: none;"> We have developed a complete theory for the calculation of the observed Stokes parameters for radiation emitted from the surface of a rapidly rotating neutron star (NS) using the oblate Schwarzschild approximation. We accounted for the rotation of the polarization plane due to relativistic effects along the path from the stellar surface to the observer. The results were shown to agree with those obtained by performing full numerical general relativistic ray-tracing with the \textsc{arcmancer} code. We showed that the obtained polarization angle (PA) profiles may differ substantially from those derived for a spherical star. We demonstrated that assuming incorrect shape for the star can lead to biased constraints for NS parameters when fitting the polarization data. Using a simplified model, we also made a rough estimate of how accurately the geometrical parameters of an accreting NS can be determined using the X-ray polarization measurements of upcoming polarimeters like the Imaging X-ray Polarimeter Explorer (IXPE) or the enhanced X-ray Timing and Polarimetry (eXTP) mission. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2009.08852v1-abstract-full').style.display = 'none'; document.getElementById('2009.08852v1-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 September, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 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">11 pages, 10 figures, accepted in A&A</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> A&A 643, A84 (2020) </p> </li> </ol> <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> </div> </div> </main> <footer> <div class="columns is-desktop" role="navigation" aria-label="Secondary">  <div class="column"> <div class="columns"> <div class="column"> <ul class="nav-spaced"> <li><a href="https://info.arxiv.org/about">About</a></li> <li><a href="https://info.arxiv.org/help">Help</a></li> </ul> </div> <div class="column"> <ul class="nav-spaced"> <li> <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" class="icon filter-black" role="presentation"><title>contact arXiv</title><desc>Click here to contact arXiv</desc><path d="M502.3 190.8c3.9-3.1 9.7-.2 9.7 4.7V400c0 26.5-21.5 48-48 48H48c-26.5 0-48-21.5-48-48V195.6c0-5 5.7-7.8 9.7-4.7 22.4 17.4 52.1 39.5 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