A High-Energy Gamma-Ray Survey of Cygnus and Cassiopeia.

A gamma-ray telescope was used to search for celestial sources at energies above several hundred MeV. Upper limits for the gamma ray emission of six strong X-ray sources are given. The atmospheric generation rate of secondary gamma rays was also determined. The gamma ray detector is a large balloon-borne gas Cherenkov detector which has been previously described. It has a sensitive area of 4.5 m2 and 20% efficiency. The instrument has an 8 deg field of view with angular resolution of about 1.5 deg. The observing program gave exposure to the galactic plane from galactic longitude of 60 degrees to 120 degrees. An excess associated with the plane was observed, but of marginal statistical significance. An upper limit for photon energies above 400 MeV is set that is about a factor of five above an extrapolation of the OSO 3 average flux for the plane away from the galactic center.