Dramatic Drop in the X-Ray Polarization of Swift J1727.8–1613 in the Soft Spectral State

Journal
Date Issued
2024
Author(s)
Svoboda, Jiří
•
Dovčiak, Michal
•
Steiner, James F.
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Kaaret, Philip
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Podgorný, Jakub
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Poutanen, Juri
•
Veledina, Alexandra
•
•
Taverna, Roberto
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Krawczynski, Henric
•
Brigitte, Maïmouna
•
Datta, Sudeb Ranjan
•
Bianchi, Stefano
•
Muñoz-Darias, Teo
•
Negro, Michela
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Rodriguez Cavero, Nicole
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Castro Segura, Noel
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Bollemeijer, Niek
•
García, Javier A.
•
Ingram, Adam
•
•
Nathan, Edward
•
Weisskopf, Martin C.
•
Altamirano, Diego
•
Baldini, Luca
•
•
•
Emami, Razieh
•
Hu, Kun
•
•
•
Petrucci, Pierre-Olivier
•
•
•
•
Yang, Yi-Jung
•
Zhang, Yuexin
DOI
Abstract
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 ≈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 ≲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.
Volume
966
Issue
2
Start page
L35
Uri
Url
Issn Identifier
2041-8205
Ads BibCode
2024ApJ...966L..35S
Rights
open.access
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