Simultaneous H.E.S.S. and Chandra observations of Sagittarius A* during an X-ray flare

TL;DR

This study presents simultaneous X-ray and gamma-ray observations of Sagittarius A* during an X-ray flare, finding no corresponding increase in gamma-ray flux, thus constraining models of particle acceleration near the black hole.

Contribution

First simultaneous H.E.S.S. and Chandra observations of Sgr A* during a flare, providing constraints on gamma-ray emission mechanisms.

Findings

X-ray flux increased by a factor of 9 during the flare.

No significant increase in TeV gamma-ray flux was observed.

Gamma-ray flux increase of 2 or more is excluded at 99% confidence.

Abstract

The rapidly varying (~10 minute timescale) non-thermal X-ray emission observed from Sgr A* implies that particle acceleration is occuring close to the event horizon of the supermassive black hole. The TeV gamma-ray source HESS J1745-290 is coincident with Sgr A* and may be closely related to its X-ray emission. Simultaneous X-ray and TeV observations are required to elucidate the relationship between these objects. We report on joint H.E.S.S./Chandra observations performed in July 2005, during which an X-ray flare was detected. Despite a factor of 9 increase in the X-ray flux of Sgr A*, no evidence is found for an increase in the TeV gamma-ray flux from this region. We find that an increase in the gamma-ray flux of a factor of 2 or greater can be excluded at a confidence level of 99%. This finding disfavours scenarios in which the keV and TeV emission are associated with the same population of accelerated particles and in which the bulk of the gamma-ray emission is produced within ~10^{14} cm (~100 R_S) of the supermassive black hole.