The illusive Geminga: What is it

Abstract

The first unassociated gamma-ray source was discovered by SAS-2 in 1973 (Kniffen, et al., 1975) and later confirmed by COS-B (Bennett, et al., 1977). Followed the announcement, there were numerous attempts to find a counterpart, and many models were developed to explain the source. Now over fifteen years later this illusive source still remains as one of the major riddles of astrophysics. The question of why an object, which is able to emit such energetic photons is so well concealed at other wavelengths, still remains to be answered. The association with the Einstein source 1E 0630+178 is the most favored (Bignami, Caraveo, and Lamb, 1983), but this cannot be considered proven. The pulsar emission model of Ruderman and Cheng (1988) is appealing in its broad applicability, but awaits observational confirmation. The EGRET (Energetic Gamma-Ray Experimental Telescope) instrument on the Gamma-Ray Observatory provides a major improvement in observational capability to better define the location and spectrum of this source, and hopefully leads to a confident identification.