325 and 610 MHz Radio Counterparts of SNR G353.6−0.7 a.k.a. HESS J1731−347

Abstract

HESS J1731$-$347 a.k.a. SNR G353.6$-$0.7 is one of the five known shell-type supernova remnants (SNRs) emitting in the very high energy (VHE, Energy $>$ 0.1 TeV) $\gamma$-ray domain. We observed this TeV SNR with the Giant Metrewave Radio Telescope (GMRT) in 1390, 610 and 325 MHz bands. In this paper, we report the discovery of 325 and 610 MHz radio counterparts of the SNR HESS J1731$-$347 with the GMRT. Various filaments of the SNR are clearly seen in the 325 and 610 MHz bands. However, the faintest feature in the radio bands corresponds to the peak in VHE emission. We explain this anti-correlation in terms of a possible leptonic origin of the observed VHE $\gamma$-ray emission. We determine the spectral indices of the bright individual filaments, which were detected in both the 610 and the 325 MHz bands. Our values range from $-$1.11 to $-$0.15, consistent with the non-thermal radio emission. We also report a possible radio counterpart of a nearby TeV source HESS J1729$-$345 from the 843 MHz Molonglo Galactic Plane Survey and the 1.4 GHz Southern Galactic Plane Survey maps. The positive radio spectral index of this possible counterpart suggests a thermal origin of the radio emission of this nearby TeV source.