Search for and Identification of Young Compact Galactic Supernova Remnants Using THOR

TL;DR

This study used high-resolution radio data from the THOR survey to identify two new young compact supernova remnants in the galaxy, addressing the gap caused by observational biases and estimating the total number of such remnants.

Contribution

It introduces a method combining radio spectral analysis and HI absorption to discover and confirm new compact SNRs, expanding the known catalog.

Findings

Identified two new compact SNRs in the galaxy.

Estimated 15-20 undetected compact SNRs remain.

Detected SNRs align with sensitivity limits and expected distributions.

Abstract

Young Supernova remnants (SNRs) with smaller angular sizes are likely missing from existing radio SNR catalogues, caused by observational constraints and selection effects. In order to find new compact radio SNR candidates, we searched the high angular resolution (25") THOR radio survey of the first quadrant of the galaxy. We selected sources with non-thermal radio spectra. HI absorption spectra and channel maps were used to identify which sources are galactic and to estimate their distances. Two new compact SNRs were found: G31.299$-$0.493 and G18.760$-$0.072, of which the latter was a previously suggested SNR candidate. The distances to these SNRs are 5.0 $\pm$ 0.3 kpc and 4.7 $\pm$ 0.2 kpc, respectively. Based on the SN rate in the galaxy or on the statistics of known SNRs, we estimate that there are 15$-$20 not yet detected compact SNRs in the galaxy and that the THOR survey area should contain three or four. Our detection of two SNRs (half the expected number) is consistent with the THOR sensitivity limit compared with the distribution of integrated flux densities of SNRs.