OBSERVATIONS OF THE CRAB PULSAR AND NEBULA BY THE EGRET TELESCOPE ON THE COMPTON-GAMMA-RAY-OBSERVATORY

The Crab pulsar and nebula were observed three times in 1991 April to June by the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Co mpton Gamma-Ray Observatory (CGRO): April 23 to May 7, May 16 to 30, a nd June 8 to 15. The results of analysis of the gamma-ray emission in the energy range from 50 MeV to more than 10 GeV are reported. The obs erved gamma-ray light curve exhibits two peaks separated in phase by 0 .40 +/- 0.02, consistent with previous observations. The total pulsed emission from the Crab pulsar is found to be well represented by a pow er-law spectrum of the form (4.11 +/- 0.16) x 10(-9)(E/274 MeV)-2.15 /- 0.04 photons cm-2 s-1 MeV-1 , softer than the spectrum measured by COS B (Clear et al. 1987). The interpulse emission has a harder spectr um than either of the pulses. The evidence for pulsed emission above 5 GeV in the EGRET data is not conclusive. Unpulsed emission in the ene rgy range 50 MeV to 5 GeV was detected, with an indication of a harden ing of the unpulsed spectrum above about 1 GeV. There was a significan t change in the light curve over the 2 months of these observations, a lthough the shape of the spectrum remained constant.