  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*.
