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±0.3 kpc and 4.7±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.
Highlights
We searched the list of 10387 radio sources from [22] to find 17 supernova remnants (SNRs)
The THOR survey covers the region of parameter space where one expects to find small/young SNRs, and is a useful data set in which to search for new
HI data are indispensable for the identification of compact galactic non-thermal sources buried in a much larger set of extragalactic sources
Summary
For a better understanding of the interstellar medium (ISM) and the evolution of our galaxy, we need to study the properties of individual supernova remnants (SNRs) and to obtain an as complete as possible sample of SNRs. The current observed number of galactic SNRs is 294 [1]. There is an apparent deficit between the number of observed and expected galactic radio SNRs [2,3]. From the [1] catalogue, the SNR with the smallest angular radius has a radius 4500. SNR G1.9+0.3 is one of the smallest galactic SNRs, and [4] finds that it is near the galactic center. With the distance to the galactic center R0 = 8.34 ± 0.16 kpc [5], the radius is 1.8 pc
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