Proposal Details - 0720022
The ultra-deep INTEGRAL legacy hard X-ray survey (amendment) (Ajello)

Proposal Abstract

We propose to complete, with 2Ms in AO7, the INTEGRAL ultra-deep observation of 6 Ms ( a total of 4 Ms was observed in AO5 and AO6 ) of the North Ecliptic Pole (NEP). Our aim is to reach, for the first time ever, the 0.1 mCrab level in the 20-60 keV band. This will extend the present source count distributions, from Swift and INTEGRAL, to a factor ~10 lower in flux and it will produce a factor >5 improvement over the final (claimed) BAT survey at 3 years. At the 0.1 mCrab level, we expect to detect >30 faint sources; this, well-defined flux-limited, sample of sources will be used to test the validity of population synthesis models which try to reproduce the X-ray background spectrum. In fact, at the 0.1 mCrab level, we expect (from the model of Gilli et al., 2006) that 6 objects (out of the >30 sources) will be Compton-thick AGN.The number of INTEGRAL detected Compton-thick AGN will thus be used to constrain the validity of such models (e.g. Treister et al. 2009). Moreover, the whole sample of sources will be used to study the dependence of the obscured-to-unobscured AGN ratio with either redshift and/or luminosity and thus to test the AGN unification model. The good high-energy response of IBIS and SPI will be used to test the presence of a high-energy (>100 keV) cut-off in the AGN spectra of the brightest objects and in the stacked spectrum of all the detected AGN. Thanks to the extensive X-ray/Optical/Infrared, pre-existing coverage, the NEP is the best extragalactic field where to fully exploit the INTEGRAL capabilities. The NEP field presents also many interesting targets for AO5 proposers, the majority of which were never observed by INTEGRAL before. The detection of a sample of faint hard X-ray sources is a unique and important result INTEGRAL can achieve and it will be a legacy project for the next decade as the first mission (e.g. Simbol-X) able to probe the micro-Crab flux range in the hard X-rays will be launched not earlier than 2013.

Observation Strategy (Recommended by TAC)

2 Ms in the standard 5x5 dithering mode centred on RA, Dec = 270.0, 66.561 (l, b = 96.384, 29.811).

Proposal grade: B

Data Rights (Recommended by TAC)

The TAC has allocated the following specific data rights to this proposal: population studies, Log N - Log S

Exposure Map

The exposure maps are in galactic coordinates and units of ksec, and the colour scale is indicated at the bottom. The green lines provide the 100 ksec contour.