Cosmic-ray-induced ionization in molecular clouds adjacent to supernova
  remnants
  Energetic gamma rays (GeV to TeV photon energy) have been detected toward
several supernova remnants (SNR) that are associated with molecular clouds. If
the gamma rays are produced mainly by hadronic processes rather than leptonic
processes like bremsstrahlung, then the flux of energetic cosmic ray nuclei (>1
GeV) required to produce the gamma rays can be inferred at the site where the
particles are accelerated in SNR shocks. It is of great interest to understand
the acceleration of the cosmic rays of lower energy (<1 GeV) that accompany the
energetic component. These particles of lower energy are most effective in
ionizing interstellar gas, which leaves an observable imprint on the
interstellar ion chemistry. A correlation of energetic gamma radiation with
enhanced interstellar ionization can thus be used to support the hadronic
origin of the gamma rays and to constrain the acceleration of ionizing cosmic
rays in SNR. Using observational gamma ray data, the primary cosmic ray proton
spectrum can be modeled for E >1 GeV, and careful extrapolation of the spectrum
to lower energies offers a method to calculate the ionization rate of the
molecular cloud.
