In.XS: project for a future spaceborne hard X-ray all-sky survey

The latest all-sky survey in hard X-ray band was performed by the HEAO-1 satellite (13 - 80 keV) with an angular resolution of 24 x 48aramin.(13) A diffuse hard X-Ray background (HXB) was detected between 3 and 50keV.(16) main scientific goal of In.XS is to resolve a large fraction of this HXB into individual sources. As no distortion by Compton up-scattering is seen in the spectrum of the microwave background,(17) the hard X-ray background is believed to be mainly due to point sources. "Type I" Active Galactic Nuclei (AGN) have softer X-ray spectra than the hard X-ray background, so other sources must be considered, like faint "Type II" or "absorbed" AGN. These could be distinguished through hard X-ray spectroscopic or hardness ratio observations. Here we present In.XS - a mission concept designed to conduct the first imaging all-sky hard X-ray (2 - 80keV)survey. The angular resolution of nearly 1arcmin and good sensitivity at high energies is provided by the latest multilayer focussing mirrors. with semiconductor-based (GaAs) arrays of detectors. We also describe the mission operations, and how the all-sky survey will be complemented by follow-up pointed observations of selected fields. The good angular resolution will allow correlations and identification with objects seen at other wavelengths. In addition, since a large fraction of the Type II AGN luminosity is emitted in the hard X-ray band, this survey will provide a large unbiased sample of the AGN population. This may provide constraints on AGN evolution through the possible observation of a turnover in deep field source statistics.