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




AuthorsZdziarski Andrzej A., Veledina Alexandra, Szanecki Michał, Green David A., Bright Joe S., Williams David R. A.

PublisherIOP Publishing Ltd

Publication year2023

JournalAstrophysical Journal Letters

Journal name in sourceASTROPHYSICAL JOURNAL LETTERS

Journal acronymASTROPHYS J LETT

Article number L45

Volume951

Issue2

Number of pages8

ISSN2041-8205

eISSN2041-8213

DOIhttps://doi.org/10.3847/2041-8213/ace2c9

Web address https://doi.org/10.3847/2041-8213/ace2c9

Self-archived copy’s web addresshttps://research.utu.fi/converis/portal/detail/Publication/180462039


Abstract

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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