Multiwavelength Searches and Spectral Aspects of 3EG Sources

More than half the sources in the Third EGRET (3EG) catalog are unidentified, having no firmly established counterparts at other wavelengths. Some of the EGRET unidentified sources have remained a mystery since the first surveys of the gamma-ray sky with the COS-B satellite. The unidentified sources generally have large error circles, and finding counterparts has often been a challenging job. A multiwavelength approach, using X-ray, optical, and radio data, is often needed to understand the nature of these sources. This technique has been used recently to find likely identifications for several EGRET sources, such as 3EG J1835+5918, 3EG J2227+6122, and the COS-B field 2CG 075+00, which overlaps with two EGRET sources 3EG J2016+3657 and 3EG J2021+3716. This article reviews multiwavelength studies of unidentified EGRET sources and their spectral energy distributions, using the above-mentioned sources as examples.