The BeppoSAX High Energy Large Area Survey (HELLAS) -- II. Number counts and X-ray spectral properties

The BeppoSAX High Energy Large Area Survey (HELLAS) has surveyed about 85 deg2 of sky in the band down to a flux of . The source surface density of at the survey limit corresponds to a resolved fraction of the X-ray background (XRB) of the order of per cent. Hardness ratio analysis indicates that the spectra of a substantial fraction of the HELLAS sources (at least one-third) are harder than a power law. This hardness may be caused by large absorbing columns. The hardness ratio analysis also indicates that many HELLAS sources may have a spectrum more complex than a single absorbed power law. A soft component, superimposed on a strongly cut-off power law, is likely to be present in several sources.