# A Possible Model for the Long-Term Flares of Sgr A*

## TL;DR

This paper models how magnetic fields influence low angular momentum accretion flows around Sgr A*, explaining observed long-term flares through shock oscillations causing luminosity variability.

## Contribution

It introduces a two-dimensional magnetohydrodynamic model showing shock oscillations as a mechanism for Sgr A*'s long-term flares, aligning with recent observational data.

## Key findings

- Shock moves between 60-170 R_g with ~5 day oscillation period.
- Luminosity varies by more than a factor of 3 due to shock dynamics.
- Model reproduces observed flare frequencies of about once per day.

## Abstract

We examine the effects of magnetic field on low angular momentum flows with standing shock around black holes in two dimensions. The magnetic field brings change in behavior and location of the shock which results in regularly or chaotically oscillating phenomena of the flow. Adopting fiducial parameters like specific angular momentum, specific energy and magnetic field strength for the flow around Sgr A*, we find that the shock moves back and forth in the range 60--170R_g, irregularly recurring with a time-scale of ~5 days with an accompanying more rapid small modulation with a period of 25 hrs without fading, where R_g is the Schwarzschild radius. The time variability associated with two different periods is attributed to the oscillating outer strong shock, together with another rapidly oscillating inner weak shock. As a consequence of the variable shock location, the luminosities vary roughly by more than a factor of 3. The time-dependent behaviors of the flow are well compatible with luminous flares with a frequency of ~one per day and bright flares occurring every ~5 -- 10 days in the latest observations by Chandra, Swift and XMM-Newton monitoring of Sgr A*.