Outbursts in Stellar Black Hole Candidates: A Time-Dependent Study of Viscous Accretion Flow

Abstract

In the accretion process around compact objects, matter needs a considerable amount of viscosity to take away its angular momentum and maintain the flow towards the compact object. There are two components that dominate the accretion flow onto black holes, one having Keplerian angular momentum distribution near equatorial plane, another low angular momentum sub-Keplerian flow surrounding the Keplerian flow. A sudden rise in viscosity in the accretion disk at a very large distance from the compact object is generally responsible for the X-ray outbursts of some stellar mass black holes. When viscosity reduces, the object tends to return to its pre-outburst quiescence stage. We have tried to mimic the rise and fall of viscosity parameter as a part of the outer boundary condition by numerical simulation procedure to study the pattern of formation and disappearance of the Keplerian disk inside an advective halo. We believe that, for the first time, our results are able to simulate the two-component advective flow dynamics during an entire X-ray outburst of a black hole candidate. Also, we see, the hysteresis effect of an outburst is caused mainly for the difference in the time duration in the formation and disappearance of the Keplerian component in the two-component flow.