Continuing search of the EGRET data for high-energy gamma-ray microsecond bursts

In the mid 1970’s Hawking (1) and Page and Hawking (2), investigated theoretically the possibility of detecting high-energy gamma rays produced by the quantum-mechanical decay of a small black hole created in the early universe. They concluded that, at the end of the life of the small black hole, it would radiate a burst of gamma rays peaked near 250 MeV with a total energy of about 1034 ergs in the order of a microsecond or less if certain details of the theory were true. The characteristics of a black hole are determined by laws of physics beyond the range of current particle accelerators; hence, the search for these short bursts of high-energy gamma rays provides at least the possibility of detecting directly the gamma rays from such bursts, and a search of the EGRET data has led to an upper limit below 5×10−2 black hole decays per pc3 yr−1, placing constraints on this and other theories predicting microsecond high-energy gamma-ray bursts.