Flares from plasmoids and current sheets around Sgr A*

TL;DR

This study uses a SANE multi-loop model to simulate near-infrared flares from Sgr A*, identifying current sheets and non-thermal particle acceleration as key mechanisms, with results aligning well with observations.

Contribution

It introduces a SANE multi-loop model approach to simulate Sgr A* flares, focusing on current sheets and non-thermal emission without relying on stable jets.

Findings

Flares are linked to particle acceleration in current sheet plasmoid chains.

Simulated light curves match observed flare durations and spectral indices.

Non-thermal emission from current sheets explains observed near-infrared flares.

Abstract

The supermassive black hole Sgr A* at the center of our galaxy produces repeating near-infrared flares that are observed by ground and space based instruments. This activity has been simulated in the past with Magnetically Arrested Disk (MAD) models which include stable jet formations. The present study uses a different approach in that it considers a Standard and Normal Evolution (SANE) multi-loop model that lacks a stable jet structure. The main objective of this research is to identify regions that contain current sheets and high magnetic turbulence, and to subsequently generate a 2.2 micron light curve generated from non-thermal particles. Additionally, we investigate the properties of the flares, in particular, their evolution during flare events, and the similarity of flare characteristics between the generated and observed light curves. 2D GRMHD simulation data from a SANE multi-loop model is employed, and thermal radiation is introduced to generate a 230 GHz light curve. Physical variables are calibrated to align with the 230 GHz observations. Current sheets are identified by analyzing toroidal currents, magnetization, plasma beta, density, and dimensionless temperatures. The evolution of current sheets during flare events is studied, and higher-energy non-thermal light curves are calculated, focusing on the 2.2 micron near-infrared range. We obtain promising 2.2 micron light curves whose flare duration and spectral index behavior align well with observations. Our findings support the association of flares with particle acceleration and nonthermal emission in current sheet plasmoid chains and in the boundary of the disk inside the funnel above and below the central black hole.