Correlation of Supernova Remnant Masers and Gamma-Ray Sources
  Supernova remnants interacting with molecular clouds are potentially exciting
systems in which to detect evidence of cosmic ray acceleration. Prominent
gamma-ray emission is produced via the decay of neutral pions when cosmic rays
encounter the nearby dense clouds. In many of the supernova remnants coincident
with gamma-ray sources, the presence of OH(1720 MHz) masers is used to identify
interaction with dense gas and to provide a kinematic distance to the system.
In this paper we use statistical tests to demonstrate that there is a
correlation between these masers and a class of GeV- to TeV-energy gamma-ray
sources coincident with interacting remnants. For pion decay, the gamma-ray
luminosity provides a direct estimate of the local cosmic ray density. We find
the cosmic ray density is enhanced by one to two orders of magnitude over the
local solar value, comparable to X-ray-induced ionization in these remnants.
The inferred ionization rates are sufficient to explain non-equilibrium
chemistry in the post-shock gas, where high columns of hydroxyl are observed.
