A1 Refereed original research article in a scientific journal
Evidence for a Black Hole Spin-Orbit Misalignment in the X-Ray Binary Cyg X-1
Authors: Zdziarski Andrzej A., Veledina Alexandra, Szanecki Michał, Green David A., Bright Joe S., Williams David R. A.
Publisher: IOP Publishing Ltd
Publication year: 2023
Journal: Astrophysical Journal Letters
Journal name in source: ASTROPHYSICAL JOURNAL LETTERS
Journal acronym: ASTROPHYS J LETT
Article number: L45
Volume: 951
Issue: 2
Number of pages: 8
ISSN: 2041-8205
eISSN: 2041-8213
DOI: https://doi.org/10.3847/2041-8213/ace2c9
Web address : https://doi.org/10.3847/2041-8213/ace2c9
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/180462039
Recently, the accretion geometry of the black hole X-ray binary Cyg X-1 was probed with the X-ray polarization. The position angle of the X-ray-emitting flow was found to be aligned with the position angle of the radio jet in the plane of the sky. At the same time, the observed high polarization degree could be obtained only for a high inclination of the X-ray-emitting flow, indicating a misalignment between the binary axis and the black hole spin. The jet, in turn, is believed to be directed by the spin axis; hence, a similar misalignment is expected between the jet and binary axes. We test this hypothesis using very long (up to about 26 yr) multiband radio observations. We find a misalignment of 20°–30°. However, contrary to the earlier expectations, the jet and binary viewing angles are found to be similar, while the misalignment is seen between the position angles of the jet and the binary axis on the plane of the sky. Furthermore, the presence of the misalignment calls into question our understanding of the evolution of this binary system.
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