A.S. Vinokurova aSpecial Astrophysical Observatory, Russian Academy of Sciences, Nizhnii Arkhyz, Zelenchukskiy Region, Karachai-Cherkessian Republic, Russian Federation bLomonosov Moscow State University, Shternberg State Astronomical Institute, Universitetskii prosp. 13, Moscow, 119889, Russian Federation
Ultraluminous X-ray sources (ULXs) that are located in external galaxies exhibit X-ray luminosities exceeding hundreds or even thousands times those of the brightest black holes in Milky Way and Local Group galaxies. New classes of objects have been discovered: ultraluminous X-ray pulsars (ULXPs) and high-velocity outflows whose X-ray-range speed is up to 0.2 c. The ULXs and ULXPs fully correspond to concepts of the super-Eddington accretion. Five ULXs exhibit in the X-range power spectra quasi-periodical oscillations and a flat-topped noise. Optical spectra of the ULXs are very similar to those of SS433, late nitrogen stars (WNL/WR) or LBV stars (luminous blue variables). The results obtained suggest that the ULXs are the systems that contain supercritical accretion disks.
Keywords: ultraluminous X-ray sources, optical spectroscopy, X-ray data, quasi-periodical oscillations PACS:97.60.Gb, 97.80.Jp, 98.70.Qy (all) DOI:10.3367/UFNe.2019.04.038595 URL: https://ufn.ru/en/articles/2019/11/g/ Citation: Fabrika S N, Atapin K E, Vinokurov A S "On the nature of ultraluminous X-ray sources" Phys. Usp.62 1162–1169 (2019)