Abstract Details

Name: Unnati Kashyap
Affiliation: Indian Institute of Technology Indore
Conference ID: ASI2021_453
Title : Testing nature of ultra-luminous X-ray source by UV-X-ray variability study of Holmberg~II X-1 using AstroSat.
Authors and Co-Authors : M. Safonova (Indian Institute of Astrophysics, Bengaluru 560034, India), U. Kashyap (Indian Institute of Technology Indore, Indore 453552, India), M. Chakraborty (Indian Institute of Technology Indore, Indore 453552, India), P.T.Rahna (CAS Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Shanghai 200030, China), O.P. Bordoloi (Tezpur University, Tezpur, Assam 784028, India), R. Gogoi (Tezpur University, Tezpur, Assam 784028, India), S. Fabrika (Special Astrophysical Observatory, Russian Academy of Sciences, Nizhny Arkhyz 369167, Russia), A. Vinokurov (Special Astrophysical Observatory, Russian Academy of Sciences, Nizhny Arkhyz 369167, Russia), O. Egorov (Special Astrophysical Observatory, Russian Academy of Sciences, Nizhny Arkhyz 369167, Russia), K. Atapin (Special Astrophysical Observatory, Russian Academy of Sciences, Nizhny Arkhyz 369167, Russia), A. Moiseev (Special Astrophysical Observatory, Russian Academy of Sciences, Nizhny Arkhyz 369167, Russia), F. Sutaria (Indian Institute of Astrophysics, Bengaluru 560034, India) and J. Murthy (Indian Institute of Astrophysics, Bengaluru 560034, India)
Abstract Type : Poster
Abstract Category : Stars, ISM and Galaxy
Abstract : The physics of ultraluminous X-ray sources (ULXs) are yet unexplained and there is no strong evidence to distinguish between their two competing models: intermediate-mass black holes (IMBHs) and supercritical accretion disks (SCADs) despite intensive studies. According to the first model, they may represent a special and elusive class of black holes (BHs) - intermediate-mass black holes (IMBHs) with masses between stellar-mass and supermassive BHs (~10^{3-4} Solar Mass) and a standard accretion disk. The second model explains ULXs to be stellar-mass BHs (~10 Solar Mass) with supercritical accretion disks (SCADs) accreting at super-Eddington rate. In this case, UV radiation is thought to be formed in the disk wind from the collimated X-ray radiation in the supercritical disk funnel. We performed simultaneous X-ray/UV observations of one of the most luminous ULX - Holmberg II X-1 with SXT and UVIT onboard ASTROSAT over multiple epochs. The main goal is to test the UV responses to the X-ray variability of the ULX. The X-ray spectra was well described by a multi-colored blackbody model and the evolution of the temperature and inner disk was obtained from the spectral fitting. Our observations show a possible correlation between X-ray and UV fluxes that indicated to either a black hole binary with the supercritical disk or a precessing disk. Thus if ULXs are SCADs, then they are the first extragalactic supercritical disks that can be observed directly. A study of such ULXs may provide a better understanding of stellar as well as supermassive black holes in supercritical regimes and also shed light on the physics of ULXs.