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   71049
   We propose the observations of transient X-ray sources in the Galactic
   Center region. In this region we have discovered the diffuse 6.4-keV
   line component, which is considered as the fluorescent K-alpha line
   from neutral iron. It should be the good tracer for hidden high energy
   activity in the region. However, the origin has not been understood,
   yet. If the transients in this region preserved the brightness for a
   few years, they would give significant contribution to the 6.4-keV
   intensity. In addition, using their column densities, we can derive the
   column density distribution more exactly where the statistics
   critically lacks at present. The exact column density distribution is
   essential to investigate the origin of 6.4-keV line distribution.
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