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   PR # 11195
    We propose to extend our highly successful ROSAT deep survey program
    to hard X-ray energies. We focus our attention on our ROSAT fields
    where we have so far spectroscopically identified 75 per cent of our
    X-ray sources. This unique database will: (i) assess the AGN contribu
    tion to the hard X-ray background by determining the X-ray spectral
    properties of the numerous, faint, high redshift AGN and by constrain
    ing the X-ray luminosity function and its evolution with redshift;
    (ii) resolve about half of the hard X-ray background and determine
    whether a population of sources other than the AGN detected in optic-
    al and ROSAT surveys contribute an appreciable fraction to the hard
    X-ray background.

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