NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-06-17 T22:28:54 PDT
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For refcode 2005ApJ...625...89K:
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Copyright by American Astronomical Society. Reproduced by permission
2005ApJ...625...89K Extragalactic Source Counts in the 20 -- 50 keV Energy Band from the Deep Observation of the Coma Region by INTEGRAL IBIS R. Krivonos, A. Vikhlinin, E. Churazov, A. Lutovinov, S. Molkov, and R. Sunyaev Abstract. We present the analysis of serendipitous sources in a deep, 500 ks, hard X-ray observation of the Coma Cluster region with the IBIS instrument on board INTEGRAL. In addition to the Coma Cluster, the final 20 -- 50 keV image contains 12 serendipitous sources with statistical significance >4 {sigma}. We use these data (after correcting for expected number of false detections) to extend the extragalactic source counts in the 20 -- 50 keV energy band down to a limiting flux of 1.0x10^-11^ ergs s^-1^ cm^-2^ (=~1 mcrab). This is a more than a factor of 10 improvement in sensitivity compared to the previous results in this energy band obtained with the HEAO 1 A-4 instrument. The derived source counts are consistent with the Euclidean relation N(>f) is proportional to f^-3/2^. A large fraction of identified serendipitous sources are low-redshift, z<0.02, active galactic nuclei (AGNs), mostly of Seyfert 1 type. The surface density of hard X-ray sources is (1.4+/-0.5)x10^-2^deg^-2^ above a flux threshold of 10^-11^ ergs s^-1^ cm^-2^. These sources directly account for ~3% of the cosmic X-ray background in the 20 -- 50 keV energy band. Given the low redshift depth of our sample, we expect that similar sources at higher redshifts account for a significant fraction of the hard X-ray background. Our field covers only 3% of the sky; a systematic analysis of other extragalactic INTEGRAL observations can produce much larger source samples and is, therefore, critically important. Keywords: Galaxies: Active, Galaxies: Seyfert, X-Rays: Diffuse Background, X-Rays: General
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