A1 Refereed original research article in a scientific journal
Dramatic Drop in the X-Ray Polarization of Swift J1727.8-1613 in the Soft Spectral State
Authors: Svoboda, Jiří; Dovčiak, Michal; Steiner, James F.; Kaaret, Philip; Podgorný, Jakub; Poutanen, Juri; Veledina, Alexandra; Muleri, Fabio; Taverna, Roberto; Krawczynski, Henric; Brigitte, Maimouna; Datta, Sudeb Ranjan; Bianchi, Stefano; Munoz-Darias, Teo; Negro, Michela; Rodriguez Cavero, Nicole; Castro Segura, Noel; Bollemeijer, Niek; Garcia, Javier A.; Ingram, Adam; Matt, Giorgio; Nathan, Edward; Weisskopf, Martin C.; Altamirano, Diego; Baldini, Luca; Capitanio, Fiamma; Egron, Elise; Emami, Razieh; Hu, Kun; Marra, Lorenzo; Mastroserio, Guglielmo; Petrucci, Pierre-Olivier; Ratheesh, Ajay; Soffitta, Paolo; Tombesi, Francesco; Yang, Yi-Jung; Zhang, Yuexin
Publisher: IOP Publishing Ltd
Publication year: 2024
Journal: Astrophysical Journal Letters
Journal name in source: ASTROPHYSICAL JOURNAL LETTERS
Article number: ARTN L35
Volume: 966
Issue: 2
ISSN: 2041-8205
eISSN: 2041-8213
DOI: https://doi.org/10.3847/2041-8213/ad402e
Publication's open availability at the time of reporting: Open Access
Publication channel's open availability : Open Access publication channel
Web address : https://iopscience.iop.org/article/10.3847/2041-8213/ad402e
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/404690963
Self-archived copy's licence: CC BY
Self-archived copy's version: Publisher`s PDF
Black hole X-ray binaries exhibit different spectral and timing properties in different accretion states. The X-ray outburst of a recently discovered and extraordinarily bright source, Swift J1727.8-1613, has enabled the first investigation of how the X-ray polarization properties of a source evolve with spectral state. The 2-8 keV polarization degree was previously measured by the Imaging X-ray Polarimetry Explorer (IXPE) to be approximate to 4% in the hard and hard intermediate states. Here we present new IXPE results taken in the soft state, with the X-ray flux dominated by the thermal accretion disk emission. We find that the polarization degree has dropped dramatically to less than or similar to 1%. This result indicates that the measured X-ray polarization is largely sensitive to the accretion state and the polarization fraction is significantly higher in the hard state when the X-ray emission is dominated by upscattered radiation in the X-ray corona. The combined polarization measurements in the soft and hard states disfavor a very high or low inclination of the system.
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