Thermal radio absorption as a tracer of the interaction of SNRs with their environments

We present new images and continuum spectral analysis for 14 resolved Galactic SNRs selected from the 74 MHz Very Large Array Low-Frequency Sky Survey Redux (VLSSr). combine integrated measurements VLSSr with flux densities extracted GLEAM literature to generate improved spectra. publicly available at 1.4 GHz, analyse morphology index distribution across each SNR. Three of SNRs, Kepler, G28.6-0.1, Tycho, have spectra which can be adequately fit simple power laws. The map Tycho confirms internal absorption was previously detected by LOFAR, but it is insufficient affect spectrum. For pulsar wind nebulae G21.5-0.9 3C58 we identify high-frequency breaks 38 12 respectively. A low frequency turnover fits data remaining nine SNRs. Kes 67, 69, Kes75, 3C397, attribute ionised gas along line sight, possibly extended HII region envelopes. W41 attributed regions located in its immediate proximity. Thermal interactions interface between SNR forward shocks surrounding medium were identified as responsible 3C391; our spectrum consistent previous results. evidence same phenomenon three additional Kes73, W49B, 3C396, derive constraints on physical properties interaction. This result indicates that their environs should readily detectable through thermal future observations sensitivity resolution.