0531000

A deep observation of the North Ecliptic Pole is proposed. The aim is to reach a factor ~10 lower in flux than achieved previously. A considerable number of new faint sources are expected which will be used to test the validity of population synthesis models which try to reproduce the X-ray background spectrum. Some of the faint sources will be Compton-thick AGN. The sample of sources will also 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. [truncated! Please see actual data for full text]