Clumpy Wind Accretion in Cygnus X-1

Abstract

Cygnus X-1 is one of the brightest X-ray sources observed and shows the X-ray intensity variations on timescales from milliseconds to months in both the soft and hard X-rays. The accretion onto the black hole is believed to be wind fed due to focused stellar wind from the binary companion HDE-226868. We aim to understand the physical mechanism responsible for the short timescale X-ray variability (<100 s) of the source in its hard/low state. We compute the 2D relativistic hydrodynamic simulation of the low angular momentum accretion flow with a time-dependent outer boundary condition that reflects the focused, clumpy wind from the supergiant in this X-ray binary system. We follow the dynamical evolution of our model for about 100 s and present the results showing an oscillatory shock, being a potential explanation of variability observed in hard X-rays. The simulated model with shock solutions is in good agreement with the observed power density spectra of the source.

On the origin of core radio emissions from black hole sources in the realm of relativistic shocked accretion flow

“…Extensive numerical simulations of the accretion disc independently confirm the formation of shocks as well (Ryu, Chakrabarti, & Molteni 1997;Fragile & Blaes 2008;Das et al 2014;Generozov et al 2014;Okuda & Das 2015;Suková & Janiuk 2015;Okuda et al 2019;Palit, Janiuk, & Czerny 2020). Due to the shock compression, the post-shock flow becomes hot and dense that results in a puffed up torus like structure which acts as the effective boundary layer of the black hole and is commonly called as post-shock corona (hereafter PSC).…”