Flares from Sgr A* and their emission mechanism

TL;DR

This paper reviews recent multi-wavelength observations of Sgr A* flares and proposes a synchrotron cooling break model as the most plausible emission mechanism, challenging inverse Compton explanations.

Contribution

It introduces a feasible synchrotron cooling break model for Sgr A* flares, replacing less realistic inverse Compton scenarios.

Findings

Synchrotron cooling break explains spectral differences between NIR and X-ray.

Magnetic field strength around 5-30 Gauss fits observed data.

Electrons cool rapidly in X-ray, slowly in NIR, producing the spectral break.

Abstract

We summarize recent observations and modeling of the brightest Sgr A* flare to be observed simultaneously in (near)-infrared and X-rays to date. Trying to explain the spectral characteristics of this flare through inverse Compton mechanisms implies physical parameters that are unrealistic for Sgr A*. Instead, a "cooling break" synchrotron model provides a more feasible explanation for the X-ray emission. In a magnetic field of about 5-30 Gauss the X-ray emitting electrons cool very quickly on the typical dynamical timescale while the NIR-emitting electrons cool more slowly. This produces a spectral break in the model between NIR and X-ray wavelengths that can explain the differences in the observed spectral indices.