Improved model of X-ray emission from hot accretion flows

TL;DR

This paper presents an advanced model of X-ray emission from hot accretion flows around black holes, incorporating detailed physics and Monte Carlo simulations to better interpret observational spectra.

Contribution

The paper introduces a comprehensive, relativistic Monte Carlo model of X-ray emission from accretion flows, including pion-decay electrons and parameter dependencies, improving upon previous models.

Findings

Model spectra depend on black hole spin, electron heating, magnetization, and accretion rate.

Joint spectral fitting can reliably constrain model parameters.

Significant differences from previous models due to improved Comptonization treatment.

Abstract

We have developed an improved model of X-ray emission from optically thin, two-temperature accretion flows, \texttt{kerrflow}, using an exact Monte Carlo treatment of global Comptonization as well as with a fully general relativistic description of both the radiative and hydrodynamic processes. It also includes pion-decay electrons, whose synchrotron emission dominates the seed photons yield at high accretion rates in flows around supermassive black holes. We consider in detail the dependence of the model spectra on the black hole spin, the electron heating efficiency, the plasma magnetization and the accretion rate, and we discuss feasibility of constraining these parameters by analyzing X-ray spectra of nearby low-luminosity active galactic nuclei. We note some degeneracies which hinder precise estimations of these parameters when individual X-ray spectra are analyzed. These degeneracies are eliminated when several spectra from a given source are fitted jointly, which then allows us to reliably measure the model parameters. We find significant differences with previous spectral models of hot-flow emission, related with the computational methods for Comptonization. Finally, we briefly consider and discuss the dependence on the viscosity parameter and on the outflow strength.