INTEGRAL/IBIS all-sky survey in hard X-rays ^*,**

¹ Max-Planck-Institute für Astrophysik, Karl-Schwarzschild-Str. 1, 85740 Garching bei München, Germany e-mail: krivonos@mpa-garching.mpg.de
² Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, 117997 Moscow, Russia

Received: 29 January 2007
Accepted: 27 July 2007

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  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 > 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 deg² 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.