Search for High Energy Gamma-ray Sources in the Southern Sky

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The supernova 1987A in the Large Magellanic Cloud has provided the first opportunity to study the emission of particles and electromagnetic radiation from a young supernova. A rapidly rotating, magnetized neutron star at the center of the expanding ejecta may be a powerful source of ultra high-energy (UHE) cosmic rays. H. Sato has pointed out that high energy gamma-rays may be produced from the decay pions generated by the collisions of hadrons accelerated by the neutron star with supernova ejecta. We installed gamma-ray detectors at the Black Birch in New Zealand (1640 m above sea level, 41ﾟ45'S, 173ﾟ47'E). The counter array consists of 76 scintillation detectors. The observations started on 13 October 1987. An upper limit on tile flux of UHE gamma-rays from SN1987A (>100 TeV) was obtained to be 4X10^<-14> cm^<-2> sec^<-1> from the data of 1987-1991. gamma-rays above 3 TeV emitted by SN1987A have been searched for using three, Cerenkov mirrors and data give an upper bound on the flux of 5X10^<-12> cm^<-2> sec^<-1>. Data on January 14 and 15 1988 were found to have excess counts corresponding to a flux of (1.9<plus-minus>0.5)X10^<-11> cm^<-2> sec^<-1>. The observed time of the excess coincides with the time of X-ray flare detected by the Ginga Satellite.Recently, we have searched for UHE gamma-ray from Southern objects including Cen A, Vela X-1, Cen X-3, Cir X-1 and also several objects in the Magellanic Clouds. None of these sources shows significant excess events. The observation is still being carried out.The moon was used to measure the angular resolution of the detector through its shadowing effect. The density of the events at the center of the moon has been found to be lower than event density near direction of the moon.