Polarized Emission from Four Supernova Remnants in the THOR Survey

Abstract

Abstract We present polarization and Faraday rotation for the supernova remnants (SNRs) G46.8 − 0.3, G43.3 − 0.2, G41.1 − 0.3, and G39.2 − 0.3 in the L-band (1–2 GHz) radio continuum in the H i/OH/Recombination line survey. We detect polarization from G46.8 − 0.3, G43.3 − 0.2, and G39.2 − 0.3 but find upper limits at the 1% level of Stokes I for G41.1 − 0.3. For G46.8 − 0.3 and G39.2 − 0.3, the fractional polarization varies on small scales from 1% to ∼6%. G43.3 − 0.2 is less polarized with fractional polarization ≲3%. We find upper limits at the 1% level for the brighter regions in each SNR with no evidence for associated enhanced Faraday depolarization. We observe significant variation in Faraday depth and fractional polarization on angular scales down to the resolution limit of 16″. Approximately 6% of our polarization detections from G46.8 − 0.3 and G39.2 − 0.3 exhibit two-component Faraday rotation and 14% of polarization detections in G43.3 − 0.2 are multicomponent. For G39.2 − 0.3, we find a bimodal Faraday depth distribution with a narrow peak and a broad peak for all polarization detections as well as for the subset with two-component Faraday rotation. We identify the narrow peak with the front side of the SNR and the broad peak with the back side. Similarly, we interpret the observed Faraday depth distribution of G46.8 − 0.3 as a superposition of the distributions from the front side and the back side. We interpret our results as evidence for a partially filled shell with small-scale magnetic field structure and internal Faraday rotation.