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   PR # 11189
    The origin of the Cosmic X-ray Background (CXB) has still remained an
    astrophysical puzzle. Now the most of the CXB flux is thought to orig
    inate from the distant faint objects in the Universe. The CXB spectra
    in 2-30 keV is, however, flatter than that of majority of the known
    sources, and cannot be explained without unknown harder emission of
    the faint objects. The previous deepest surveys was ineffective above
    3 keV, so that they could not exactly resolve this puzzle. The ASCA
    opens the way observationally to research the origin of the hard
    emission of the faint objects up to 1E-14 erg cmE-2 sE-1 (2-10 keV),
    which is comparable with the limit of the previous deep survey below
    3keV.We would propose the deep sky survey on the ASCA detection limit
   in the Selected Area 57.
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