| we present the analysis of serendipitous sources in a deep , 500 ksec , hard x - ray observation of the coma cluster region with the ibis instrument onboard _ integral_. in addition to the coma cluster , the final 2050 kev image contains 12 serendipitous sources with statistical significance @xmath0 . we use these data ( after correcting for expected number of false detections ) to extend the extragalactic source counts in the 2050 kev energy band down to a limiting flux of @xmath1 ( @xmath2 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 a4 instrument . the derived source counts are consistent with the euclidean relation , @xmath3 . a large fraction of identified serendipitous sources are low - redshift , @xmath4 agns , mostly of seyfert 1 type . the surface density of hard x - ray sources is @xmath5 per square degree above a flux threshold of @xmath6 . these sources directly account for @xmath7 of the cosmic x - ray background in the 2050 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 . |