THE 22 MONTHSWIFT-BAT ALL-SKY HARD X-RAY SURVEY

We present the catalog of sources detected in the first 22 months of data from the hard X-ray survey (14-195 keV) conducted with the Burst Alert Telescope (BAT) coded mask imager on the Swift satellite. The catalog contains 461 sources detected above the 4.8 sigma level with BAT. High angular resolution X-ray data for every source from Swift-XRT or archival data have allowed associations to be made with known counterparts in other wavelength bands for over 97% of the detections, including the discovery of similar to 30 galaxies previously unknown as active galactic nuclei and several new Galactic sources. A total of 266 of the sources are associated with Seyfert galaxies (median redshift z similar to 0.03) or blazars, with the majority of the remaining sources associated with X-ray binaries in our Galaxy. This ongoing survey is the first uniform all-sky hard X-ray survey since HEAO-1 in 1977. Since the publication of the nine-month BAT survey we have increased the number of energy channels from four to eight and have substantially increased the number of sources with accurate average spectra. The BAT 22 month catalog is the product of the most sensitive all-sky survey in the hard X-ray band, with a detection sensitivity (4.8 sigma) of 2.2 x 10(-11) erg cm(-2) s(-1) (1 mCrab) over most of the sky in the 14-195 keV band.