A Disc-Corona Model for a Rotating Black Hole

TL;DR

This paper introduces a new disc-corona model around Kerr black holes incorporating magnetic torque effects, deriving analytical power expressions, numerically solving the system, and simulating spectra to explore parameter influences.

Contribution

It presents a novel analytical and numerical model of a disc-corona system with magnetic torque around rotating black holes, including spectral simulations.

Findings

Magnetic torque significantly increases energy release in the system.

The corona power fraction rises with black hole spin parameter.

Spectral output depends on system parameters and is simulated via Monte Carlo.

Abstract

We propose a disc-corona model in which a geometrically thin, optically thick disc surrounds a Kerr black hole, and magnetic fields exert a time-steady torque on the inner edge of the accretion disc. The analytical expression of the total gravitational power is derived from the thin-disc dynamics equations by using this new boundary condition. It is shown that the magnetic torque can considerably enhance the amount of energy released in the disc-corona system. Furthermore, the global solutions of this disc-corona system are obtained numerically. We find that the fraction of the power dissipated into the corona in the total for such disc-corona system increases with the increasing dimensionless black hole spin parameter $a_\ast $, but is insensitive on the $\Delta \varepsilon $ which is the additional radiative efficiency parameter relevant to magnetic torque, for $\Delta\varepsilon > 1$. In addition, the emerged spectra from this disc-corona system are simulated by using Monte-Carlo method, and the effect of the different parameters on the output spectra is discussed.