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   PR #   112
   The Lockman Hole is a sky area at which direction HI column densityis
   extremely low (5e19 cm-2). Thus, it has been considered to be the best
   window to observe extragalactic sources at EUV and soft X-ray bands.In
   fact the ROSAT PSPC detected about ninety sources in 20 arcmin radius
   field. Intensities of the sources were down to 0.28e-14 erg/s/cm2.
   Deep exposure at the Lockman Hole with ASCA will provide us spectraand
   number density of faintest sources never detected in medium energy
   X-rayband. In connection with the ROSAT result, we will get wide band
   X-ray spectra of those sources from 0.1 to 10 keV. Furthermore,
   spatialfluctuation, which possibly exists, also give us important
   information onthe origin of cosmic X-ray background.
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