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   81714
   We successfully detected a time variability of the hard component in
   M82 from ASCA AO-4, which directly implies that its origin is a massive
   BH. However, the spectrum of the hard component does not agree with
   that of AGN. Additionally, there is no correlation between the
   temperature and luminosity in M82, suggesting that the hard component
   is not an ULX. The hard component could be a new type of BHs. Thus, we
   propose a long term continuous observation of M82 to investigate the
   nature of the massive BH. 1) We determine the mass of the BH by using
   the NPSD. 2) We search for a periodicity. 3) We track the changes of X-
   ray luminosity and temperature and look for a possible relationship
   between the two. 4) We investigate time variabilities of iron 6.4 and
   6.7 keV lines.
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