Low angular momentum flow model II for Sgr A*

TL;DR

This study models low angular momentum, two-temperature accretion flows around Sgr A* using 1D and 2D hydrodynamical simulations, revealing nearly adiabatic behavior, shock oscillations, and variability potentially linked to observed flares.

Contribution

It introduces a detailed two-temperature accretion flow model around Sgr A* incorporating recent stellar wind data and explores shock dynamics and variability through hydrodynamical simulations.

Findings

Flow remains nearly adiabatic despite cooling processes.

Luminosity depends on magnetic energy ratio, reaching 10^{35}-10^{36} erg/s.

Shocks form and oscillate, causing luminosity and outflow variability.

Abstract

We examine 1D two-temperature accretion flows around a supermassive black hole, adopting the specific angular momentum \lambda, the total specific energy \epsilon and the input accretion rate \dot M_{input} = 4.0x10^{-6} solar mass/yr estimated in the recent analysis of stellar wind of nearby stars around Sgr A*. The two-temperature flow is almost adiabatic even if we take account of the heating of electrons by ions, the bremsstrahlung cooling and the synchrotron cooling, as long as the ratio \beta of the magnetic energy density to the thermal energy density is taken to be as \beta < 1. The different temperatures of ions and electrons are caused by the different adiabatic indices of ions and electrons which depend on their temperature states under the relativistic regime. The total luminosity increases with increasing \beta and results in - 10^{35} - 10^{36} erg/s for \beta=10^{-3} - 1. Furthermore, from 2D time-dependent hydrodynamical calculations of the above flow, we find that the irregularly oscillating shocks are formed in the inner region and that the luminosity and the mass-outflow rate vary by a factor of 2 -- 3 and 1.5 -- 4, respectively. The time variability may be relevant to the flare activity of Sgr A*.