  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.
