Thermal Equilibria of Optically Thin, Magnetically Supported, Two-Temperature, Black Hole Accretion Disks

TL;DR

This paper presents thermal equilibrium solutions for optically thin, magnetically supported, two-temperature black hole accretion disks, explaining the bright/hard state with stable, low-beta magnetic configurations at high accretion rates.

Contribution

It introduces magnetically supported, thermally stable solutions for two-temperature accretion disks, incorporating magnetic fields and radiative processes, explaining observed X-ray states.

Findings

Low-beta solutions are thermally stable.

High luminosities are explained by magnetic support.

Electron temperatures are moderately cool.

Abstract

We obtained thermal equilibrium solutions for optically thin, two-temperature black hole accretion disks incorporating magnetic fields. The main objective of this study is to explain the bright/hard state observed during the bright/slow transition of galactic black hole candidates. We assume that the energy transfer from ions to electrons occurs via Coulomb collisions. Bremsstrahlung, synchrotron, and inverse Compton scattering are considered as the radiative cooling processes. In order to complete the set of basic equations, we specify the magnetic flux advection rate. We find magnetically supported (low-beta), thermally stable solutions. In these solutions, the total amount of the heating via the dissipation of turbulent magnetic fields goes into electrons and balances the radiative cooling. The low-$\beta$ solutions extend to high mass accretion rates and the electron temperature is moderately cool. High luminosities and moderately high energy cutoffs in the X-ray spectrum observed in the bright/hard state can be explained by the low-beta solutions.