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   81506
   With ASCA, we found a new category of X-ray objects, "X-ray reflection
   nebula" Sgr B2. This source is characterized by very strong 6.4-keV
   line from neutral iron, and it is considered that the giant molecular
   cloud is irradiated by an external X-ray source and emits only
   fluorescent and reflected X-rays. However, there is no strong X-ray
   source around Sgr B2. The most clear explanation for this probrem is
   that the Galactic nucleus Sgr A* had been bright, but is currently dim.
   To confirm this hypothesis, we propose to observe Sgr C cloud, which
   also emits strong 6.4-keV line and new candidate of the "X-ray
   reflection nebula". By studying the time variability of this source, we
   can verify whether the Sgr C is "X-ray reflection nebula" or not.
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