Observation of gamma-radiation from the galactic center region

A balloon-borne investigation of the region in the vicinity of the galactic center was performed with a y-ray telescope having an angular resolution of about 1% above 15 MeV. A narrow band of emission about 3 wide, lying along the galactic equator, was observed over the atmospheric background, and confirms the detection of galactic y-radiation first observed above 100 MeV from OSO-3. The integral intensity above 15 MeY is about 3.5 x 10- y cm 2 1 rad-1, but is dependent on the assumed spectrum. A comparison with the measurements above 100 MeV indicates that at least 50 percent of the radiation comes from the decay of 7rO mesons produced in cosmicray collisions on interstellar gas. The possibility that point sources also contribute to this excess cannot be ruled out; however, we are unable to confirm the existence of any of the reported y-ray sources within 20 of the galactic center. Our results suggest that either these suspected sources are variable or they have hard emission spectra (e.g., 7TO decay). Subject headings: cosmic rays gamma rays - interstellar matter - X-ray sources