The Suzaku Hard X-ray Survey on the Galactic Center Region
  Diffuse X-rays from the Galactic center (GC) region were found to exhibit
many K-shell lines from iron and nickel atoms in the 6--9 keV band. The strong
emission lines seen in the spectrum are neutral iron K$\alpha$ at 6.4~keV,
He-like iron K$\alpha$ at 6.7~keV, H-like iron Ly$\alpha$ at 6.9~keV, and
He-like iron K$\beta$ at 7.8~keV. Among them, the 6.4~keV emission line is a
probe of non-thermal phenomena. We have detected strong 6.4~keV emission in
several giant molecular clouds, some of which were newly discovered by Suzaku.
All the spectra exhibit large equivalent widths of 1-2~keV and absorption
columns of $2-10\times 10^{23}\{\rm H\ cm}^{-2}$. We found time variability of
diffuse 6.4~keV emission in the Sgr B2 region comparing the maps and spectra
obtained from 1994 to 2005 with ASCA, Chandra, XMM-Newton and Suzaku. We also
report discovery of K$\alpha$ lines of neutral argon, calcium, chrome, and
manganese atoms in the Sgr~A region. We show that the equivalent width of the
6.4~keV emission line detected in X-ray faint region against the 6.4
keV-associated continuum (power-law component) is $\sim 800\ {\rm eV}$. These
features are naturally explained by the X-ray reflection nebula scenario rather
than the low energy cosmic-ray electrons scenario. On the other hand, a 6.4~keV
clump, G~0.162$-$0.217, discovered at the south end of the Radio Arc has a
small equivalent width of 6.4~keV emission line of $\sim200\ {\rm eV}$. The
Radio Arc is a site of relativistic electrons. Thus, it is conceivable that the
X-rays of G~0.162$-$0.217 are due to low energy cosmic-ray electrons
