Alexander Kolodzig, Marat Gilfanov, Rashid Sunyaev, Sergey Sazonov, Marcella Brusa
Context. The main element of the observing program of the Spectrum-Roentgen-Gamma orbital observatory is a 4-years all-sky survey in the course of which the entire sky will be scanned eight times. Aims. We analyze statistical properties of AGN and QSOs to be detected in the course of the eROSITA all-sky survey (eRASS). Methods. Given the currently planned survey strategy, parameters of the galactic and extragalactic X-ray background and results of the recent calculations of the eROSITA instrumental background, we compute the sensitivity map of the eRASS. Using the best available redshift-dependent AGN X-ray luminosity function (XLF) we compute various characteristics of the eRASS AGN sample, such as the luminosity and redshift distributions and the brightness distributions of their optical counterparts. Results. After four years of the survey, the sky-average sensitivity of ~10^(-14) erg s^(-1) cm^(-2) will be achieved in the 0.5-2.0 keV band. With this sensitivity, eROSITA will detect about ~3 million of AGN on the extragalactic sky (|b| > 10 deg). The median redshift of the eRASS AGN will be z = 1 with ~40% of objects in the z = 1 - 2 redshift range. There will be about ~ 10^4 - 10^5 AGN beyond redshift z = 3 and about ~ 2 000 - 30 000 AGN beyond redshift z = 4, the exact numbers depending on the poorly known behavior of the AGN XLF in the high redshift and luminosity regimes. The 10% of brightest AGN will be detected with more than ~38 counts per PSF HEW, whereas the 10% of faintest objects will have less than ~9 counts. The optical counterparts of about ~95% of AGN will be brighter than I_(AB) = 22.5mag. The planned scanning strategy will allow one to search for transient events on the time scale of a half a year and a ~few hours with the 0.5-2.0 keV sensitivity of ~ 2 x 10^(-14) - ~ 2 x 10^(-13) erg s^(-1) cm^(-2) respectively.
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http://arxiv.org/abs/1212.2151
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