Detection of Sub-TeV Gamma Rays from the Galactic Center Direction by CANGAROO-II

We have detected sub-TeV gamma-ray emission from the direction of the Galactic center (GC) using the CANGAROO-II Imaging Atmospheric Cerenkov Telescope. We detected a statistically significant excess at energies greater than 250 GeV. The flux was 1 order of magnitude lower than that of the Crab Nebula at 1 TeV with a soft spectrum proportional to E-4.6±0.5. The signal centroid is consistent with the GC direction, and the observed profile is consistent with a pointlike source. Our data suggest that the GeV source 3EG J1746-2851 is identical to this TeV source, and we study the combined spectra to determine the possible origin of the gamma-ray emission. We also obtain an upper limit on the cold dark matter density in the Galactic halo.