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

TL;DR

This paper investigates shock formation and oscillations in low angular momentum accretion flows around black holes, linking theoretical models with observed variability in X-ray luminosity of sources like Sgr A* and stellar-mass black holes.

Contribution

It derives conditions for shock formation in quasi-spherical, slightly rotating flows and confirms these with numerical simulations, explaining observed luminosity variability.

Findings

Shock oscillations match observed flare timescales.

Hysteresis loops occur in flows with varying angular momentum.

Models explain periodic X-ray luminosity oscillations in black hole systems.

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 hydro-simulations, 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 timescales 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.