### Results of a southern-hemisphere search for gamma-ray sources at E/sub gamma/greater than or equal to3times10$sup 11$ eVResults of a southern-hemisphere search for gamma-ray sources at E/sub gamma/greater than or equal to3times10$sup 11$ eV

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 Author Grindlay, J. E. ♦ Helmken, H. F. ♦ Brown, R. H. ♦ Allen, L. R. Source United States Department of Energy Office of Scientific and Technical Information Content type Text Language English
 Subject Keyword Physics (Astrophysics & Cosmology)-Quasi-stellar, Radio & X-Ray Sources ♦ Physics (Astrophysics & Cosmology)-Stars ♦ Physics (Astrophysics & Cosmology)-Galaxies ♦ Physics Research-Astrophysics & Cosmology-Quasi- Stellar, Radio & X-Ray Sources ♦ COSMIC GAMMA SOURCES- GAMMA RADIATION ♦ CHERENKOV RADIATION ♦ COSMIC X-RAY SOURCES ♦ GALAXIES ♦ MUONS ♦ PULSARS ♦ SUPERNOVAE Abstract The optical intensity interferometer operated by Sydney University at Narrabri, NSW, Australia, was converted in 1972 April to a sensitive detector of atmospheric Cerenkov light from extensive air showers (EAS) with E$sub 0$>2times10$sup 11$ eV. Its two 7-m aperture optical reflectors were separated by 120 m and pointed by computer at the mean altitude for the maximum development of EAS from the direction of an object to be studied. Off-axis photomultipliers on the reflectors viewed the atmospheric Cerenkov light from EAS muon cores, thus enabling rejection of greater than or equal to50 percent of EAS detected as being cosmic-ray-initiated. Possible (greater than or equal to3 sigma) sources were found in 1972 in the directions of Cen A (NGC 5128), the Vela Pulsar, and MP 1451, out of 11 candidate objects studied. The objects included pulsars, unusual X-ray sources, active galaxies, a supernova, and lower energy (approx.100 MeV) $gamma$-ray sources such as the galactic center. (Confirmation of the 1972 results was attempted in an improved series of observations in 1973 April-June and 1974 March-April. The Cen A result was confirmed and is reported elsewhere. Upper limits are given here for the other objects, together with evidence for a variable for a variable pulsed flux from the Vela Pulsar. Implications of the results are discussed. (AIP) Educational Use Research Learning Resource Type Article Publisher Date 1975-10-01 Publisher Place United States Journal Astrophys. J. Volume Number 201 Issue Number 1 Organization Center for Astrophysics, Harvard College Observatory and Smithsonian Astrophysical Observatory