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   PR # 21192
    We propose a survey observation of a large sky area, 3.3deg2, to flux
    limit of 6e-14 erg/cm2/sec in AO-2. Optical follow-up will be made   
    along with the observation. The flux limit is much deeper than large-
    area/all sky surveys available to now, and the area is substantially 
    larger than the ROSAT Deep Survey so far achieved. We expect 100 sour
    ces in AO-2. The unique features are the observation in a higher ener
    gy band, with which we expect different sky from ROSAT's. The scienti
    fic goal is "X-ray cosmology" with a deep X-ray selected catalogue.  
    Specific aims are multifold with immediate interests including logS- 
    logN relation, luminosity function, evolution and large scale cluster
    ing of QSO/AGN's, and evolution of galaxy clusters, fluctuation and  
   large scale structure of CXB. 
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