K-shell Emission of Neutral Iron Line from Sgr B2 Excited by
  Subrelativistic Protons
  We investigated the emission of K$\alpha$ iron line from the massive
molecular clouds in the Galactic center (GC). We assume that at present the
total flux of this emission consists of time variable component generated by
primary X-ray photons ejected by Sagittarius A$^\ast$ (Sgr A$^\ast$) in the
past and a relatively weak quasi-stationary component excited by impact of
protons which were generated by star accretion onto the central black hole. The
level of background emission was estimated from a rise of the 6.4 keV line
intensity in the direction of several molecular clouds, that we interpreted as
a stage when the X-ray front ejected by Sgr A$^\ast$ entered into these clouds.
The 6.4 keV emission before this intensity jump we interpreted as emission
generated by subrelativistic cosmic rays there. The cross-section of K$\alpha$
vacancies produced by protons differs from that of electrons or X-rays.
Therefore, we expect that this processes can be distinguished from the analysis
of the equivalent width of the iron line and time variations of the width can
be predicted. The line intensity from the clouds depends on their distance from
Sgr A$^\ast$ and the coefficient of spacial diffusion near the Galactic center.
We expect that in a few years the line intensity for the cloud G\,0.11$-$0.11
which is relatively close to Sgr A$^\ast$ will decreases to the level
$\lesssim$ 10% from its present value. For the cloud Sagittarius B2 (Sgr B2)
the situation is more intricate. If the diffusion coefficient $D\gtrsim
10^{27}$ cm$^2$ s$^{-1}$ then the expected stationary flux should be about 10%
of its level in 2000. In the opposite case the line intensity from Sgr B2
should drop down to zero because the protons do not reach the cloud.
