On the nature of ultraluminous X-ray sources

LEANDRO ABAROA; GUSTAVO E. ROMERO

Buenos Aires

Workshop; 1st. Padova ? Buenos Aires Workshop on Massive stars and Interacting Binaries; 2024

IAFE - UBA

Ultraluminous X-ray sources (ULXs) are extragalactic point-like objects where the X-ray luminosity appears to be higher than the Eddington luminosity. ULXs are thought to be X-ray binaries with a compact stellar-mass object accreting at super-Eddington rates, where the accretion disk launches powerful winds. A beaming effect could be responsible for the observed X-ray luminosity: the radiation emitted from the inner part of the accretion disk is geometrically collimated by the ejected wind, which is optically thick except for a narrow region around the black hole axis, forming a cone-shaped funnel. Furthermore, in some ULXs the emission extends to energies higher than 10 keV that cannot be produced in the disk, and the hard X-rays require an additional component. Such a component could be a hot plasma of relativistic electrons in the funnel above the black hole that Comptonize the softer photons from the disk, producing the non thermal tail. In this talk we will present the state-of-the-art on ULXs from a theoretical approach and show some recent results, focusing in particular on their super-Eddington nature.