The Burst and Transient Source Experiment (BATSE) Earth Occultation Catalog of Low-Energy Gamma-Ray Sources

The Burst and Transient Source Experiment (BATSE), aboard the Compton Gamma Ray Observatory (CGRO), provided a record of the low-energy gamma-ray sky (~20-1000 keV) between 1991 April and 2000 May (9.1 yr).

BATSE monitored the high-energy sky using the Earth occultation technique (EOT) for point sources whose emission extended for times on the order of the CGRO orbital period (~92 min) or greater. Using the EOT to extract flux information, a catalog of sources using data from the BATSE Large Area Detectors has been prepared. The first part of the catalog consists of results from the all-sky monitoring of 58 sources, mostly Galactic, with intrinsic variability on timescales of hours to years. For these sources, we have included tables of flux and spectral data, and outburst times for transients. Light curves (or flux histories) have been placed on the World Wide Web.

We then performed a deep-sampling of these 58 objects, plus a selection of 121 more objects, combining data from the entire 9.1 yr BATSE data set. Source types considered were primarily accreting binaries, but a small number of representative active galaxies, X-ray-emitting stars, and supernova remnants were also included. The sample represents a compilation of sources monitored and/or discovered with BATSE and other high-energy instruments between 1991 and 2000, known sources taken from the HEAO 1 A-4 and Macomb & Gehrels catalogs. The deep sample results include definite detections of 83 objects and possible detections of 36 additional objects. The definite detections spanned three classes of sources: accreting black hole and neutron star binaries, active galaxies, and supernova remnants. The average fluxes measured for the fourth class, the X-ray emitting stars, were below the confidence limit for definite detection.

Flux data for the deep sample are presented in four energy bands: 20-40, 40-70, 70-160, and 160-430 keV. The limiting average flux level (9.1 yr) for the sample varies from 3.5 to 20 mcrab (5 σ) between 20 and 430 keV, depending on systematic error, which in turn is primarily dependent on the sky location.

To strengthen the credibility of detection of weaker sources (~5-25 mcrab), we generated Earth occultation images, searched for periodic behavior using FFT and epoch folding methods, and critically evaluated the energy-dependent emission in the four flux bands. The deep sample results are intended for guidance in performing future all-sky surveys or pointed observations in the hard X-ray and low-energy gamma-ray band, as well as more detailed studies with the BATSE EOT.