ROSAT Deep Surveys

Abstract

AbstractA series of 20 deep pointed observations with the ROSAT PSPC is discussed. 530 X-ray sources with 0.5-2 keV fluxes down to 3·10-15erg cm-2 s-1 have been discovered in 5.9 deg2. The N(>S) relation of the sources selected in the 0.5-2 keV band shows a density in excess of 200 deg-2 at the faintest fluxes and a flattening below 2·10-14erg cm-2 s-1. The average spectrum of those sources is a power law with energy index 1.2 ±0.1. The absorption column densities are consistent with the galactic HI columns. More than 50% of the 1-2 keV background has been resolved into discrete sources in the deepest field. The total background spectrum shows an emission line feature around 0.65 keV, most probably due to OVII-OVIII from a 2·106K plasma. Above ~ 1 keV the background is dominated by a power law spectrum with a normalization of 13.4 ± 0.2 keV cm-2 s-1 sr-1 keV-1 and a slope 1.2 ± 0.1, i.e. considerably steeper than the extrapolation from higher energies.