NH$_3$(3,3) and CH$_3$OH near Supernova Remnants: GBT and VLA Observations

TL;DR

This study uses GBT and VLA observations to detect NH3 and CH3OH masers near supernova remnants, revealing high-density gas regions that may be linked to cosmic ray interactions and gamma-ray emission.

Contribution

It demonstrates that NH3 and CH3OH masers serve as effective indicators of dense, shocked gas in supernova remnant environments, providing new density estimates.

Findings

NH3 and CH3OH masers are detected in most observed SNRs.

Masers are associated with high-density gas (~10^5 cm^-3).

Masers are located close to SNR shock fronts, indicating shocked dense clumps.

Abstract

We report on Green Bank Telescope 23.87 GHz NH$_3$(3,3), emission observations in five supernova remnants interacting with molecular clouds (G1.4$-$0.1, IC443, W44, W51C, and G5.7$-$0.0). The observations show a clumpy gas density distribution, and in most cases the narrow line widths of $\sim3-4$\,km\,s$^{-1}$ are suggestive of maser emission. Very Large Array observations reveal 36~GHz and/or 44~GHz CH$_3$OH, maser emission in a majority (72\%) of the NH$_3$, peak positions towards 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 CH$_3$OH, and NH$_3$, maser emission can be used as indicators of high density clumps of gas shocked by supernova remnants, and provide density estimates thereof. Modeling of the optical depth of the NH$_3$(3,3) emission is compared to that of CH$_3$OH, constraining the densities of the clumps to a typical density of the order of $10^5$~cm$^{-3}$ 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.