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Wind-powered Ultraluminous X-ray Sources

Wiktorowicz, Grzegorz and Lasota, Jean-Pierre and Belczynski, Krzysztof and Lu, Youjun and Liu, Jifeng and Iłkiewicz, Krystian (2021) 'Wind-powered Ultraluminous X-ray Sources.', The Astrophysical Journal, 918 (2). p. 60.


Although ultraluminous X-ray sources (ULX) are important for astrophysics because of their extreme apparent super-Eddington luminosities, their nature is still poorly known. Theoretical and observational studies suggest that ULXs could be a diversified group of objects that are composed of low-mass X-ray binaries, high-mass X-ray binaries and marginally also systems containing intermediate-mass black holes. Observational data on the ULX donors could significantly boost our understanding of these systems, but only a few have been detected. There are several candidates, mostly red supergiants (RSGs), but surveys are typically biased toward luminous near-infrared objects. In ULXs harbouring RSGs matter accreted onto the compact body would have to be provided by the stellar wind of the companion because a Roche-lobe overflow could be unstable for relevant mass-ratios. We present a comprehensive study of the evolution and population of wind-fed ULXs, and we provide a theoretical support for the link between RSGs and ULXs. Assuming a minimal model of stellar-wind emission, our estimated upper limit on contribution of wind-fed ULX to the overall ULX population is ∼75%–96% for young (<100 Myr) starforming environments, ∼49%–87% for prolonged constant star formation (e.g., disk of Milky Way), and 1% for environments in which star formation ceased long time (>2 Gyr) ago. We show also that some wind-fed ULXs (up to 6%) may evolve into merging double compact objects (DCOs). We demonstrate that the exclusion of wind-fed ULXs from population studies of ULXs might have lead to systematic errors in their conclusions.

Item Type:Article
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Publisher statement:© 2021. The American Astronomical Society. All rights reserved.
Date accepted:18 June 2021
Date deposited:14 October 2021
Date of first online publication:08 September 2021
Date first made open access:14 October 2021

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