Discovery of interacting molecular gas toward the TeV gamma-ray peak of the SNR G 347.3-0.5

Supernova remnants (= SNR) are suggested to be sites of cosmic-ray acceleration. In particular, it has been an issue of keen interest whether cosmic ray protons are being accelerated in a SNR which emits TeV gamma-rays. A crucial observational test for this is to find dense molecular gas towards the SNR, because such molecular gas can best verify the existence of cosmic-ray protons via pion decay to gamma-rays. Here, we show that new high-resolution mm-wave observations of interstellar CO molecule have revealed molecular gas at 1 kpc distance interacting with the TeV gamma-ray SNR G 347.3-0.5, and that a molecular cloud of similar to 200 solar masses is clearly associated with the TeV gamma-ray peak. providing strong evidence for proton acceleration. We have estimated the total energy of accelerated protons to be similar to 1048 erg, which corresponds to an acceleration efficiency of similar to 0.001, posing an observational constraint on the proton acceleration.