Origin of Hydrogen Ionization in the 1 pc Galactic Central Region
  We study a possible connection between processes of gamma-ray emission and
hydrogen ionization in a few pc of central region around Sgr A*. Previous
investigations showed there is a discrepancy between interpretation of
gamma-ray and ionization data if gamma-rays are generated by proton-proton
collisions. Here we provided analysis of processes of ionization and emission
basing on analytical and numerical calculations of kinetic equations which
describe processes of particle propagation and their energy losses. The origin
of gamma rays could be either due to collisions of relativistic protons with
the dense gas of the surrounding circumnuclear disk (CND) or bremsstrahlung and
inverse Compton scattering of relativistic electrons. The hydrogen ionization
in this case is produced by a low energy component of the CR spectrum. We found
that if ionization is produced by protons the expected ionization rate of
hydrogen in the CND is of the same order as derived from IR observations. So we
do not see any discrepancy between the gamma-ray and ionization data for the
hadronic model. In the case of ionization by electrons we obtained the
ionization rate one order of magnitude higher than follows from the IR data. In
principle, a selection between the leptonic and hadronic interpretations can be
performed basing on measurements of radio and X-ray fluxes from this region
because the leptonic and hadronic models give different values of the fluxes
from there. We do not exclude that gamma-ray production and hydrogen ionization
in the CND are due to a past activity of Sgr A* which occurred about 100 year
ago. Then we hypothesize that there may be connection between a past proton
eruption and a flux of hard X-rays emitted by Sgr A* hundred years ago as
follows from the observed time variability of the iron line seen in the
direction of GC molecular clouds.
