A Survey of Hydroxyl Toward Supernova Remnants: Evidence for Extended 1720 MHz Maser Emission

TL;DR

This study uses GBT observations to reveal that extended, low-level OH maser emission is common in supernova remnants interacting with molecular clouds, providing insights into the physical conditions of such interactions.

Contribution

It demonstrates that extended OH maser emission is prevalent in SNRs and models the physical conditions of the excited OH gas.

Findings

Extended maser emission is common in SNRs.

Physical conditions include low column densities, moderate temperatures, and high densities.

Single dish observations detect more flux than interferometry.

Abstract

We present the results of GBT observations of all four ground-state hydroxyl (OH) transitions toward 15 supernova remnants (SNRs) which show OH(1720 MHz) maser emission. This species of maser is well established as an excellent tracer of an ongoing interaction between the SNR and dense molecular material. For the majority of these objects we detect significantly higher flux densities with a single dish than has been reported with interferometric observations. We infer that spatially extended, low level maser emission is a common phenomenon that traces the large-scale interaction in maser-emitting SNRs. Additionally we use a collisional pumping model to fit the physical conditions under which OH is excited behind the SNR shock front. We find the observed OH gas associated with the SNR interaction having columns less than approximately 10^17 per square cm, temperatures of 20 to 125 K, and densities 10^5 per cubic cm.