INTEGRAL/IBIS all-sky survey in hard X-rays

Abstract

We present results of an all-sky hard X-ray survey based on almost four years of observations with the IBIS telescope onboard the INTEGRAL observatory. The dead time-corrected exposure of the survey is ∼33 Ms. Approximately 12% and 80% of the sky has been covered to limiting fluxes lower than 1 and 5 mCrab, respectively. Our catalog of detected sources includes 403 objects, 316 of which exceed a 5σ detection threshold on the time-averaged map of the sky, and the rest were detected in various subsamples of exposures. Among the identified sources, 219 are Galactic (90 low-mass X-ray binaries, 76 high-mass X-ray binaries, 21 cataclysmic variables, 6 coronally active stars, and other types) and 137 are extragalactic, including 130 active galactic nuclei (AGNs) and 3 galaxy clusters. We derived number-flux functions of AGNs and Galactic sources. The log N log S relation of non-blazar AGNs is based on 68 sources located at Galactic latitudes |b| > 5°, where the survey is characterized by high identification completeness, with fluxes higher than Slim = 1.1 × 10-1 erg s-1 cm-2 (∼0.8 mCrab) in the 17-60 keV energy band. The cumulative AGN number-flux function can be described by a power law with a slope of 1.62 ±0.15 and normalization of (5.7 ±0.7) × 10-3 sources per deg2 at fluxes > 1.43 × 10-1 erg s-1 cm-2 (>1 mCrab). Those AGNs with fluxes higher than Slim make up ∼1% of the cosmic X-ray background at 17-60 keV. We present evidence of strong inhomogeneity in the spatial distribution of nearby (≲70 Mpc) AGNs, which reflects the large-scale structure in the local Universe. © ESO 2007.