The third EGRET catalog of high-energy gamma-ray sources

The third catalog of high-energy gamma-ray sources detected by the EGRET te lescope on the Compton Gamma Ray Observatory includes data from 1991 April 22 to 1995 October 3 (cycles 1, 2, 3, and 4 of the mission). In addition to including more data than the second EGRET catalog and its supplement, this catalog uses completely reprocessed data (to correct a number of mostly mi nimal errors and problems). The 271 sources (E > 100 MeV) in the catalog in clude the single 1991 solar flare bright enough to be detected as a source, the Large Magellanic Cloud, five pulsars, one probable radio galaxy detect ion (Cen A), and 66 high-confidence identifications of blazars (BL Lac obje cts, flat-spectrum radio quasars, or unidentified hat-spectrum radio source s). In addition, 27 lower confidence potential blazar identifications are n oted. Finally, the catalog contains 170 sources not yet identified firmly w ith known objects, although potential identifications have been suggested f or a number of those. A figure is presented that gives approximate upper li mits for gamma-ray sources at any point in the sky, as well as information about sources listed in the second catalog and its supplement, that do not appear in this catalog.