Particle Acceleration and the Origin of X-ray Flares in GRMHD simulations of Sgr A*

TL;DR

This study uses GRMHD simulations with non-thermal electrons to explain the origin and variability of X-ray flares in Sgr A*, linking magnetic reconnection regions near the event horizon to observed IR and X-ray flaring behavior.

Contribution

It introduces a simulation framework incorporating non-thermal electrons motivated by PIC results to explain Sgr A*'s flaring activity and variability.

Findings

X-ray variability arises from non-thermal electrons in magnetized regions

X-ray flares are always coincident with IR flares, but not vice versa

Simulation results align qualitatively with observed flare patterns

Abstract

Significant X-ray variability and flaring has been observed from Sgr A* but is poorly understood from a theoretical standpoint. We perform GRMHD simulations that take into account a population of non-thermal electrons with energy distributions and injection rates that are motivated by PIC simulations of magnetic reconnection. We explore the effects of including these non-thermal electrons on the predicted broadband variability of Sgr A* and find that X-ray variability is a generic result of localizing non-thermal electrons to highly magnetized regions, where particles are likely to be accelerated via magnetic reconnection. The proximity of these high-field regions to the event horizon forms a natural connection between IR and X-ray variability and accounts for the rapid timescales associated with the X-ray flares. The qualitative nature of this variability is consistent with observations, producing X-ray flares that are always coincident with IR flares, but not vice versa, i.e., there are a number of IR flares without X-ray counterparts.