Results of a Southern-Hemisphere search for gamma-ray sources at energies of at least 300 GeV

Abstract

Results are reported for a series of observations of possible high-energy gamma-ray sources in the Southern Hemisphere. The observations were made using the Narrabri optical intensity interferometer as a sensitive detector of Cerenkov light from extensive air showers initiated by high-energy gamma rays. The candidate sources included Cen A, the Vela pulsar, supernova 1972e, quasar 3C 273, the galactic center, and Cen X-3, as well as several other pulsars and X-ray sources. Upper flux limits for each object are presented together with equivocal evidence for a variable pulsed flux from the Vela pulsar. The results of the survey show that detectable sources exist at photon energies in excess of 100 GeV and that a number of sources of hard X-rays and 100-MeV gamma rays are not strong sources of high-energy gamma rays.