EGRET DETECTION OF HIGH-ENERGY GAMMA-RAYS FROM THE GAMMA-RAY BURST OF 3 MAY 1991

On May 3, 1991, the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory detected a gamma-ray burst both in the energy measurement subsystem and independently in the spark chamber assembly. Six individual photons were detected in the spark chamber, allowing a determination of the burst arrival direction which was l(II) = 171.9-degrees +/- 1.3-degrees, b(II) = 5.3-degrees +/- 1.1-degrees. Three energy spectra were measured from 1 to 200 MeV; they were measured during the first second after the BATSE trigger, the next two seconds and the subsequent four seconds. The first two spectra exhibit a similar differential spectra index of about -2.2 with no apparent high-energy cut-off. By the time of the third spectrum, and additional soft component is evident.