Upper limit for ultra-high-energy gamma rays from SN 1987A obtained by Cerenkov technique at large zenith angles

The supernova SN 1987A has been observed with the JANZOS cosmic-ray facility at the Black Birch Range in New Zealand since October 1987. From May to July 1988, observations were carried out using the Cerenkov telescope at a zenith angle of 68 deg. By working at large zenith angles, the effective detection area and energy threshold are both increased. From 39 hr or greater of observation, an upper bound of 5.7 x 10 to the -14th/sq cm sec on the flux of gamma rays with energies of 75 TeV is obtained at the 95-percent confidence level. This flux limit corresponds to the gamma ray luminosity of 10 to the 37th ergs/sec. 20 refs.