Three-dimensional Radiative Properties of Hot Accretion Flows onto the Galactic Centre Black Hole

TL;DR

This study models the three-dimensional radiative properties of accretion flows onto the Galactic Centre black hole, explaining observed spectra and emission features across radio to X-ray frequencies with thermal electron processes.

Contribution

It presents a comprehensive 3D radiative transfer analysis of accretion flows onto Sgr A*, incorporating synchrotron and bremsstrahlung emissions to match observations.

Findings

Core radio emission is larger than the event horizon shadow.

Self-absorbed synchrotron emission explains low-frequency spectra.

Bremsstrahlung emission accounts for X-ray spectra in different states.

Abstract

By solving radiative transfer equations, we examine three-dimensional radiative properties of a magnetohydrodynamic accretion flow model confronting with the observed spectrum of Sgr A*, in the vicinity of supermassive black hole at the Galactic centre. As a result, we find that the core of radio emission is larger than the size of the event horizon shadow and its peak location is shifted from the gravitational centre. We also find that the self-absorbed synchrotron emissions by the superposition of thermal electrons within a few tens of the Schwartzschild radius can account for low-frequency spectra below the critical frequency $\nu_{c}\approx 10^{12}$ Hz. Above the critical frequency, the synchrotron self-Compton emission by thermal electrons can account for variable emissions in recent near-infrared observations. In contrast to the previous study by Ohsuga et al. (2005), we found that the X-ray spectra by Bremsstrahlung emission of thermal electrons for the different mass accretion rates can be consistent with both the flaring state and the quiescent state of Sgr A* observed by {\it Chandra}.