0586062 - ASÚ 2025 RIV US eng J - Journal Article
Svoboda, Jiří - Dovčiak, Michal - Steiner, J.F. - Kaaret, P. - Podgorný, Jakub - Brigitte, Maimouna - Datta, Sudeb Ranjan … Total 37 authors
Dramatic drop in the X-ray polarization of Swift J1727.8-1613 in the soft spectral state.
Astrophysical Journal Letters. Roč. 966, č. 2 (2024), č. článku L35. ISSN 2041-8205. E-ISSN 2041-8213
R&D Projects: GA ČR(CZ) GX21-06825X
Institutional support: RVO:67985815
Keywords : black hole physics * X-ray astronomy * polarimetry
OECD category: Astronomy (including astrophysics,space science)
Impact factor: 7.9, year: 2022
Method of publishing: Open access

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.
Permanent Link: https://hdl.handle.net/11104/0353686