Search for discrete sources of cosmic gamma rays of energy 1011 to 1012 eV

Twenty-seven celestial sources have been examined for high-energy -ray emission in the previously unexplored region of the electromagnetic spectrum from I0 to t0 eV. An optical reflector of 10-m aperture was used to detect Cerenkov radiation from cosmic-ray air showers; showers induced by - rays from a discrete source would be apparent as a directional anisotropy. The principal source investigated was the Crab Nebula. Others included supernova remnants, radio galaxies, quasars, magnetic variable stars, pulsars, and X-ray sources, with particular emphasis on M87, M82, 3C 273, and Sgr A No statistically significant effects were detected, although there was the possibility of a flux associated with the pulsar NP 0532 following the period jump in 1969 September. The observations also suggest a lower limit to the average magnetic field in the Crab Nebula of 6 X 10- gauss.