High-Energy Cosmic Gamma-Ray Observations from the OSO-3 Satellite

Final results from observations carried out in 1967-1968 with an instrument on the OSO-3 satellite confirm the discovery of cosmic y-rays with energies above 50 MeV. The celestial distribution demonstrates the existence of a galactic component which is concentrated in a band of directions around the galactic equator with a broad maximum toward the galactic center. It also shows the existence of an isotropic component with a softer energy spectrum which is probably of extragalactic origin. Using calibration results derived from new measurements on the flight backup instrument, we find for the integral equivalent line intensity above 100 MeV of the galactic center component in the region -15 < b21 < 15 , - 30 I < 30 a peak value (isotropic component subtracted) of 1.3 x 10- (cm2 s rad) -`, and for the general galactic component in the region -15 < b" < 15,30 111< value 3.4 x 10-5(cm2srad)-1.Theintensity of the isotropic component is 3.0 x 10-2 (cm s sterad) i. (The known statistical and systematic uncertainty in these values is approximately 30 percent, but additional systematic uncertainty of a factor of 2 cannot be excluded.) The galactic-latitude distribution of events away from the galactic center region matches the distribution predicted for the detector on the assumption that the general galactic intensity is proportional to the columnar density of interstellar neutral gas deduced from 21-cm radio measurements. The absolute intensity of this component can be accounted for if one assumes that y-rays with E > 100 IeV are produced by the 7rO process at a rate of 1.6 x 10-22 1 per atom of neutral hydrogen.