Soft gamma-ray constraints on a bright flare from the Galactic Center supermassive black hole

TL;DR

This paper reports the first simultaneous soft gamma-ray, X-ray, near-infrared, and mid-infrared observations of a bright flare from Sagittarius A*, providing new constraints on emission mechanisms near the black hole's horizon.

Contribution

It presents the first multiwavelength coverage including soft gamma-rays of a flare from Sgr A*, offering new insights into the emission processes at play.

Findings

Detected a bright flare in X-ray and near-infrared with simultaneous soft gamma-ray and mid-infrared data.

Derived upper limits on the spectral energy distribution at gamma-ray and mid-infrared wavelengths.

Discussed emission mechanisms such as synchrotron, synchrotron self-Compton, and external Compton processes.

Abstract

Sagittarius A* (Sgr A*) is the supermassive black hole residing at the center of the Milky Way. It has been the main target of an extensive multiwavelength campaign we carried out in April 2007. Herein, we report the detection of a bright flare from the vicinity of the horizon, observed simultaneously in X-rays (XMM/EPIC) and near infrared (VLT/NACO) on April 4th for 1-2 h. For the first time, such an event also benefitted from a soft gamma-rays (INTEGRAL/ISGRI) and mid infrared (VLT/VISIR) coverage, which enabled us to derive upper limits at both ends of the flare spectral energy distribution (SED). We discuss the physical implications of the contemporaneous light curves as well as the SED, in terms of synchrotron, synchrotron self-Compton and external Compton emission processes.