Low angular momentum flow model of Sgr A* activity

TL;DR

This paper proposes a hybrid low angular momentum accretion flow model for Sgr A*, combining Bondi and MHD simulations, to better explain its variability and observed spectra.

Contribution

It introduces a new hybrid model of low angular momentum accretion flow combining spherical and MHD components for Sgr A*.

Findings

The model fits the broad band observational data of Sgr A*.

Low angular momentum flow explains variability better.

The flow's radiation spectrum matches observations.

Abstract

Sgr A* is the closest massive black hole and can be observed with the highest angular resolution. Nevertheless, our current understanding of the accretion process in this source is very poor. The inflow is almost certainly of low radiative efficiency and it is accompanied by a strong outflow and the flow is strongly variable but the details of the dynamics are unknown. Even the amount of angular momentum in the flow is an open question. Here we argue that low angular momentum scenario is better suited to explain the flow variability. We present a new hybrid model which describes such a flow and consists of an outer spherically symmetric Bondi flow and an inner axially symmetric flow described through MHD simulations. The assumed angular momentum of the matter is low, i.e. the corresponding circularization radius in the equatorial plane of the flow is just above the innermost stable circular orbit in pseudo-Newtonian potential. We compare the radiation spectrum from such a flow to the broad band observational data for Sgr A*.