SEARCH FOR ULTRA-HIGH-ENERGY RADIATION FROM GAMMA-RAY BURSTS

Using data from the CYGNUS extensive air shower array, we have searched for evidence of emission of ultra-high-energy radiation coincident with [gamma]-ray bursts observed by the BATSE instrument on the Compton Gamma-Ray Observatory. No statistically significant excess was found for any point in the sky within 4[sigma] of BATSE's best location coordinates for any of the 56 bursts examined. Furthermore, no events were seen in the 2.2[degree] radius circular bin surrounding [gamma]-ray burst GRB 920720, whose location was determined accurately by the Compton/Ulysses/PVO Interplanetary Network of satellites. Flux upper limits depend greatly on the actual zenith angle of the burst. Typical fluence upper limits above 100 TeV are [approximately]10[sup [minus]6] erg cm[sup [minus]2]. The fluence upper limits for GRB 920720 is 2 [times] 10[sup [minus]6] erg cm[sup [minus]2].