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R. C. Hartman (NASA/GSFC), EGRET Team
The Third EGRET Catalog has been accepted for publication in the ApJ Supplements. Its covers CGRO Cycles 1-4 (1991 April 22 to 1995 October 3), the entire time that EGRET operated in its normal wide-field-of-view mode. The Catalog contains 271 sources, a substantial increase over the sum of the Second Catalog (Thompson et al. 1995 - 2EG) and the Second Catalog Supplement (Thompson et al. 1996 - 2EGS). This is due to the inclusion of Cycle 4 (not covered in 2EG or 2EGS), use of maps of the summed data for the entire time period as well as those for individual observations, and use of a slightly different analysis technique that decreases the source detection threshold somewhat. The 271 sources in the catalog include one solar flare, six gamma-ray pulsars, the Large Magellanic Cloud, one possible detection of a radio galaxy (Cen A ), 67 strong identifications of blazars and flat-spectrum radio sources, and 27 possible blazar detections. There are 169 unidentified sources, 79 of them within 10 degrees of the Galactic plane. The "cloud" of apparent sources within 30 degrees of the Galactic Center, seen in 2EG+2EGS, is even more obvious in this catalog; it appears to be somewhat more dense to the north of the Galactic plane.