A parametrization to test black hole candidates with the spectrum of thin disks

TL;DR

This paper introduces a simple parametrization of deviations from the Kerr metric to efficiently test black hole candidates using the spectrum of thin accretion disks, enabling faster numerical analysis.

Contribution

It proposes a new, computationally efficient parametrization of black hole metrics that can describe a variety of deviations from Kerr and is suitable for spectral analysis.

Findings

The parametrization can model black holes with high radiative efficiency.

It allows for rapid numerical calculations of thin disk spectra.

The approach facilitates testing deviations from Kerr in observational data.

Abstract

We discuss a parametrization to describe possible deviations from the Kerr metric and test astrophysical black hole candidates with electromagnetic radiation. Our metric is a very simple generalization of the Kerr solution with two main properties: $i)$ the phenomenology is quite rich and, for example, it can describe black holes with high Novikov-Thorne radiative efficiency or black holes of very small size; $ii)$ it is suitable for the numerical calculations required to study the spectrum of thin disks. The latter point is our principal motivation to study such a kind of parametrization, because in the analysis of real data there are usually several parameters to fit and the problem with current non-Kerr metrics is that the calculation times are too long.