Two temperature viscous accretion flows around rotating black holes: Description of under-fed systems to ultra-luminous X-ray sources

TL;DR

This paper models two-temperature viscous accretion flows around rotating black holes, exploring how disk properties and luminosities vary with parameters, and compares theoretical results with observed X-ray sources including AGNs and ULXs.

Contribution

It introduces a detailed analysis of two-temperature accretion disks around rotating black holes considering sub-Keplerian flows and varying viscosity, providing insights into observed luminosities of different astrophysical sources.

Findings

Hotter disks around rotating black holes compared to Schwarzschild black holes.

Disk properties vary significantly with viscosity parameter.

Theoretical luminosities match observed values for AGNs and ULXs.

Abstract

We discuss two temperature accretion disk flows around rotating black holes. As we know that to explain observed hard X-rays the choice of Keplerian angular momentum profile is not unique, we consider the sub-Keplerian regime of the disk. Without any strict knowledge of the magnetic field structure, we assume the cooling mechanism is dominated by bremsstrahlung process. We show that in a range of Shakura-Sunyaev viscosity parameter $0.2\gsim\alpha\gsim0.0005$, flow behavior varies widely, particularly by means of the size of disk, efficiency of cooling and corresponding temperatures of ions and electrons. We also show that the disk around a rotating black hole is hotter compared to that around a Schwarzschild black hole, rendering a larger difference between ion and electron temperatures in the former case. With all the theoretical solutions in hand, finally we reproduce the observed luminosities ($L$) of two extreme cases -- the under-fed AGNs and quasars (e.g. Sgr $A^*$) with $L\gsim 10^{33}$ erg/sec to ultra-luminous X-ray sources with $L\sim 10^{41}$ erg/sec, at different combinations of mass accretion rate, ratio of specific heats, Shakura-Sunyaev viscosity parameter and Kerr parameter, and conclude that Sgr $A^*$ may be an intermediate spinning black hole.