Oscillating shocks in the low angular momentum flows as a source of variability of accreting black holes

Abstract

We derive the conditions for shock formation in a quasi-spherical, slightly rotating flows. We verify the results of semi-analytical, stationary calculations with the time evolution studied by numerical hydrosimulations, and we study the oscillations of the shock position. We also study the behaviour of flows with varying specific angular momentum, where the 'hysteresis' type of loop is found when passing through the multiple sonic points region. Our results are in agreement with the time-scales and shapes of the luminosity flares observed in Sgr A*. These models may also be applicable for the Galactic stellar-mass black holes, like GX 339-4 or GRS 1915+105, where periodic oscillations of X-ray luminosity are detected.