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Simultaneous HESS and Chandra observations of Sagitarius A (cid:2) during an X-ray ﬂare

, ABSTRACT The rapidly varying ( ∼ 10 min timescale) non-thermal X-ray emission observed from Sgr A (cid:2) implies that particle acceleration is occuring close to the event horizon of the supermassive black hole. The TeV γ -ray source HESSJ1745 − 290 is coincident with Sgr A (cid:2) 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 HESS / 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 (cid:2) , no evidence is found for an increase in the TeV γ -ray ﬂux from this region. We ﬁnd that an increase in the γ -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 γ -ray emission is produced within ∼ 10 14 cm ( ∼ 100 R S ) of the supermassive hole.