A1 Refereed original research article in a scientific journal
Orbital variability of polarized X-ray radiation reflected from a companion star in X-ray binaries
Authors: Ahlberg, Varpu; Kravtsov, Vadim; Poutanen, Juri
Publisher: EDP SCIENCES S A
Publishing place: LES ULIS CEDEX A
Publication year: 2024
Journal: Astronomy and Astrophysics
Journal name in source: ASTRONOMY & ASTROPHYSICS
Journal acronym: ASTRON ASTROPHYS
Article number: A220
Volume: 688
Number of pages: 8
ISSN: 0004-6361
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202450131
Web address : https://doi.org/10.1051/0004-6361/202450131
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/457748026
The reflection of X-ray radiation produced near a compact object from its stellar companion contributes to the orbital variability of polarization in X-ray binaries. The X-rays are reflected mainly via Thomson scattering resulting in a high polarization. The orbital variability of the polarization strongly depends on the inclination and the orbital parameters allowing us to constrain them. To explore this phenomenon, we present analytical single-scattering models for the polarized reflection. We find that while diluted by the direct emission, the reflection can produce a polarization degree of about 1% in the case of a large reflection albedo. We fitted the orbital variations of the X-ray polarization observed by the Imaging X-ray Polarimetry Explorer from an accreting weakly magnetized neutron star "clocked burster" GS 1826-238 and found that the amplitude of the variations is too large to be primarily caused by the companion star. The polarized reflection is more significant if the compact object is obscured from the observer, and thus it should be more easily observable in certain high-inclination targets.
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Funding information in the publication:
This research has been supported by the Academy of Finland grants 333112 (JP), 355672 (VA), and by Finnish Cultural Foundation (VK)
