Discovery of the Radio and X-Ray Counterpart of TeV γ-Ray Source HESS J1731-347

Abstract

We discover a faint shell-type radio and X-ray source, G353.6-0.7, associated with HESS J1731-347. G353.6-0.7 is likely an old supernova remnant (SNR), based on radio (0.8, 1.4, and 5 GHz), infrared (8 μm from the GLIMPSE Legacy Project and 21 μm from the Midcourse Space Experiment), and X-ray (0.1-2.4 keV from the ROSAT survey and 5-20 keV from the INTEGRAL survey) data. The SNR, centered at (l, b) = (353.55°, -0.65°) with a radius of ~0.25°, closely matches the outline of the recently discovered extended TeV source HESS J1731-347, which has no previously identified counterpart. A diffuse X-ray enhancement detected in the ROSAT all-sky survey is coincident with lower half-shell of the SNR. Therefore the SNR is the best radio counterpart of both the HESS source and the diffuse X-ray enhancement. G353.6-0.7 has an age of ~27,000 yr. Altogether, the new discovery provides the best case that an old SNR emits TeV γ-rays.