Spectral signatures of dissipative standing shocks and mass outflow in presence of Comptonization around a black hole

TL;DR

This paper investigates how mass outflows and Compton cooling influence the spectral properties of accretion flows around black holes, demonstrating that increased cooling causes shock inward movement and spectral softening.

Contribution

It introduces a modified shock model incorporating mass loss and Compton cooling effects, linking outflow rates with spectral state changes in black hole accretion flows.

Findings

Cooling enhances with higher accretion rates.

Shock moves inward as cooling increases.

Outflow rate decreases with cooling.

Abstract

Accretion flows having positive specific energy are known to produce outflows and winds which escape to a large distance. According to Two Component Advective Flow (TCAF) model, centrifugal pressure dominated region of the flow just outside the black hole horizon, with or without shocks, acts as the base of this outflow. Electrons from this region are depleted due to the wind and consequently, energy transfer rate due to inverse Comptonization of low energy photons are affected. Specifically, it becomes easier to cool this region and emerging spectrum is softened. Our main goal is to show spectral softening due to mass outflow in presence of Compton cooling. To achieve this, we modify Rankine-Hugoniot relationships at the shock front when post-shock region suffers mass loss due to winds and energy loss due to inverse Comptonization. We solve two-temperature equations governing an accretion flow around a black hole which include Coulomb exchange between protons and electrons and other major radiative processes such as bremsstrahlung and thermal Comptonization. We then compute emitted spectrum from this post-shock flow. We also show how location of standing shock which forms outer boundary of centrifugal barrier changes with cooling. With an increase in disc accretion rate $(\dot{m_d})$, cooling is enhanced and we find that the shock moves in towards the black hole. With cooling, thermal pressure is reduced, and as a result, outflow rate is decreased. We thus directly correlate outflow rate with spectral state of the disc.