High-Energy Gamma-Ray Astronomy

The search for gamma radiation with energy greater than 50 Mev from extraterrestrial sources has resulted in some of the most interesting and most difficult balloon and spacecraft experiments. The present status of this search is reviewed. The first attempt to detect this radiation from solar flares resulted in no increase of the counting rate above background intensity. An upper limit of 1.0 ?? 10-2 photons cm-2 sec-1 in the type 2 flare of March 13, 1962, and an upper limit of 1.2 ?? 10-2 photons cm-2 sec-1 in the type 3 flare of March 22, 1962, was determined for the gammaray flux. The upper limit to the flux from the quiet sun was 1.0 ?? 10-2 photons cm-2 sec-1. These results represent a partial reduction of the data from the first Orbiting Solar Observatory. Of all methods used in gathering information about the nature of the universe, that of detecting and analyzing the electromagnetic wave spectrum provides the most direct and useful data. One of the most interesting and perhaps the most difficult region of the spectrum to explore is high-energy gamma radiation, which consists of photons of energy greater than 50 million electron volts. This paper will review the present status of gamma-ray astronomy and report some of the preliminary results obtained from the Orbiting Solar Observatory (OSO-I).