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

TL;DR

This study presents simultaneous H.E.S.S. and Chandra observations of Sgr A* during an X-ray flare, finding no corresponding increase in TeV gamma-ray flux, thus constraining models of gamma-ray origin near the black hole.

Contribution

First simultaneous X-ray and TeV gamma-ray observations of Sgr A* during a flare, providing constraints on gamma-ray emission models.

Findings

X-ray flux increased by over 10 times during the flare.

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

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

Abstract

The rapidly varying non-thermal X-ray emission observed from Sgr A* points to particle acceleration taking place close to the supermassive black hole. The TeV gamma-ray source HESS J1745-290 is coincident with Sgr A* and may be closely related to the X-ray emission. Simultaneous X-ray and TeV observations are required to elucidate the relationship between these two objects. Here we report on joint H.E.S.S./Chandra observations in July 2005, during which an X-ray flare was detected. Despite a factor >10 increase in the X-ray flux of Sgr A*, no evidence is found for an increase in the TeV gamma-ray flux. We find that an increase of the gamma-ray flux of a factor 2 or greater can be excluded at a confidence level of 99%. This finding disfavours scenarios in which the bulk of the gamma-ray emission observed is produced close to Sgr A*.