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    PR # 31284                                                                   
     We propose a survey observation of a large sky area, 6.6deg2, to flux       
      limit of 6e-14 erg/cm2/sec in AO-3. Optical follow-up is being 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 200 sour       
     ces in AO-3. 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. S       
     pecific aims are multifold with immediate interests including logS-lo       
     gN relation, luminosity function, evolution and large scale clusterin       
     g of QSO/AGN's, and evolution of galaxy clusters, fluctuation and lar       
    ge scale structure of CXB.                                                   
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