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   51272
   Observational results suggesting the existence of a massive black hole
   at the Galactic center has been accumulating (e.g. Genzel et al. 1996).
   ASCA also suggested the presence of the past AGN activity, from the hot
   plasma and 6.4 keV line at the molecular cloud (Koyama et al. 1996).
   Time variability of the center, if any would be more direct evidence of
   the black hole. However, previous results of the time variability now
   became controversial, because Maeda et al (1996) discovered variable
   binary source (eclipsing buster) in the vicinity of the galactic
   center. ASCA can only detect the galactic center X-rays at present.
   Thus we propose to monitor the Galactic center after September 1994.
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