INTEGRAL IBIS Census of the Sky Beyond 100 keV

We report on the first census of INTEGRAL IBIS detections (≳4 σ significance) above 100 keV based on the Core Program and public open-time observations up to 2005 April. There are 49 sources detected in the 100-150 keV band, of which 14 are also seen in the 150-300 keV range. The low-energy sample is dominated by X-ray binary systems of both low and high mass but also includes 10 active galaxies. Of the binary systems that are detected above 150 keV, more than 50% are associated with black hole candidates, often reported as microquasars. The present survey results are then used to construct log N-log S curves for galactic and extragalactic objects in the 100-150 keV band: above a 1 mcrab sensitivity limit we expect that around 200 galactic sources and almost 350 active galaxies populate the sky above 100 keV. While the contribution of individual point sources to the total Galactic emission has been estimated to be around 70%-80% between 100 and 300 keV, we find that active galaxies detected above 1 mcrab account for only about 3% of the cosmic hard X-ray background in the 100-150 keV band.