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 logN–logS 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 S lim = 1.1 × 10 −11 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 deg 2 at fluxes >1.43 × 10 −11 erg s −1 cm −2 (>1 mCrab). Those AGNs with fluxes higher than S lim 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.