2016ApJ...826..189M

We report on Green Bank Telescope 23.87 GHz NH₃(3,3) emission observations in five supernova remnants (SNRs) interacting with molecular clouds (G1.4-0.1, IC 443, W44, W51C, and G5.7-0.0). The observations show a clumpy gas density distribution, and in most cases the narrow line widths of ∼3-4 km/s are suggestive of maser emission. Very Large Array observations reveal 36 and/or 44 GHz CH₃OH maser emission in a majority (72%) of the NH₃ peak positions toward three of these SNRs. This good positional correlation is in agreement with the high densities required for the excitation of each line. Through these observations we have shown that CH₃OH and NH₃ maser emission can be used as indicators of high-density clumps of gas shocked by SNRs, and provide density estimates thereof. Modeling of the optical depth of the NH₃(3,3) emission is compared to that of CH₃OH, constraining the densities of the clumps to a typical density of the order of 10⁵/cm3 for cospatial masers. Regions of gas with this density are found to exist in the post-shocked gas quite close to the SNR shock front, and may be associated with sites where cosmic rays produce gamma-ray emission via neutral pion decay.