Properties of magnetically supported dissipative accretion flow around black holes with cooling effects

TL;DR

This paper explores the structure of magnetically supported, dissipative accretion flows around black holes, focusing on shock formation, cooling effects, and their impact on luminosity and spectra, revealing conditions for shock existence and their observational signatures.

Contribution

It presents a comprehensive analysis of shock solutions in magnetized, cooling accretion flows, identifying critical dissipation parameters and their effects on shock stability and luminosity.

Findings

Shock solutions exist under certain dissipation conditions.

Shock luminosity exceeds shock-free flow luminosity.

Shock disappearance occurs beyond critical dissipation thresholds.

Abstract

We investigate the global structure of the advection dominated accretion flow around a Schwarzschild black hole where the accretion disc is threaded by toroidal magnetic fields. We consider synchrotron radiative process as an effective cooling mechanism active in the flow. With this, we obtain the global transonic accretion solutions by exploring the variety of boundary conditions and dissipation parameters, namely accretion rate (${\dot m}$) and viscosity ($\alpha_B$). The fact that depending on the initial parameters, steady state accretion flows can possess centrifugally supported shock waves. These global shock solutions exist even when the level of dissipation is relatively high. We study the properties of shock waves and observe that the dynamics of the post-shock corona (hereafter, PSC) is regulated by the flow parameters. Interestingly, we find that shock solution disappears completely when the dissipation parameters exceed their critical values. We calculate the critical values of viscosity parameter ($\alpha^{\rm cri}_B$) adopting the canonical values of adiabatic indices as $\gamma=4/3$ (ultra-relativistic) and $1.5$ (semi-non-relativistic) and find that in the gas pressure dominated domain, $\alpha^{\rm cri}_B \sim 0.4$ for $\gamma=4/3$ and $\alpha^{\rm cri}_B \sim 0.27$ for $\gamma=1.5$, respectively. We further show that global shock solutions are relatively more luminous compared to the shock free solutions. Also, we have calculated the synchrotron spectra for shocked solutions. When the shock is considered to be dissipative in nature, it would have an important implication as the available energy at PSC can be utilized to power the outflowing matter escaped from PSC. Towards this, we calculate the maximum shock luminosity and discuss the observational implication of our present formalism.