EGRET is the high-energy gamma-ray telescope on the
Compton Observatory. Descriptions and capabilities of the
instrument are given by Hughes et al. (1980), Kanbach et al.
(1988), Kanbach (1989), and Thompson et al. (1993a). The
telescope covers the energy range from about 30 MeV to over 20
GeV. EGRET records gamma-ray photons individually as
electron-positron pair production events, which are
processed automatically (with manual verification) to
provide the arrival direction and energy of each photon. The point spread function is energy-dependent, having a FWHM of approximately 5
at 100 MeV and smaller values at higher energies.
The arrival time of each gamma ray is recorded in Universal
Coordinated Time (UTC) to an accuracy of better than 100
s. The field of view of EGRET extends to more than 30
from the instrument axis, although the sensitivity at angles beyond 30
is less than 15% of the on-axis sensitivity. Because of the low flux level of the high energy gamma rays, observing periods are typically 2-3
weeks.
The first EGRET catalog ([Fichtel et al. 1994b]) covered Phase 1 of the Compton Gamma Ray Observatory (CGRO) viewing program which began shortly after launch of the observatory on 1991 April 5 and ended on 1992 November 17. That catalog included solar flares, pulsars, gamma-ray bursts, normal galaxies, active galaxies, and unidentified sources. It listed both positive detections and upper limits for other sources thought to be of interest. In this catalog, there are two important new aspects. First, it includes Phase 2 which ran from the end of Phase 1 until 1993 September 7. Second, all of the results have now been analyzed in as consistent a manner as possible using an improved calculation of the diffuse radiation ([Bertsch et al. 1993b]; [Hunter et al. 1995]). No additional solar flares were seen during Phase 2; therefore, the first EGRET catalog summary has not been updated in the present work. Only one additional gamma-ray burst was seen by EGRET in Phase 2. Details of that burst (the ``Super Bowl'' burst) are given by Sommer et al. (1994).
This paper begins with a brief summary of the observations and the approach to the analysis, with references to the relevant papers for details. This discussion is followed in section 3 with a description of the current catalog. It differs from the first catalog in that the majority of the sources are listed in one table in order of increasing right ascension regardless of the type of source, in order to conform to conventions commonly used. There is an additional table for sources which appeared in the first EGRET catalog but do not appear here. A new approach to upper limits which will permit the reader to determine an approximate upper limit for any source is given in section 5.