A DETAILED STUDY OF THE MOLECULAR AND ATOMIC GAS TOWARD THE γ-RAY SUPERNOVA REMNANT RX J1713.7-3946: SPATIAL TeV γ-RAY AND INTERSTELLAR MEDIUM GAS CORRESPONDENCE

RX J1713.7-3946 is the most remarkable TeV gamma-ray supernova remnant (SNR) that emits gamma-rays in the highest energy range. We have made a new combined analysis of CO and H I in the SNR and derived the total protons in the interstellar medium (ISM). We have found that the inclusion of the H I gas provides a significantly better spatial match between the TeV gamma-rays and ISM protons than the H-2 gas alone. In particular, the southeastern rim of the gamma-ray shell has a counterpart only in the H I. The finding shows that the ISM proton distribution is consistent with the hadronic scenario that cosmic-ray (CR) protons react with ISM protons to produce the gamma-rays. This provides another step forward for the hadronic origin of the gamma-rays by offering one of the necessary conditions missing in the previous hadronic interpretations. We argue that the highly inhomogeneous distribution of the ISM protons is crucial in the origin of the gamma-rays. Most of the neutral gas was likely swept up by the stellar wind of an OB star prior to the supernova (SN) explosion to form a low-density cavity and a swept-up dense wall. The cavity explains the low-density site where the diffusive shock acceleration of charged particles takes place with suppressed thermal X-rays, whereas the CR protons can reach the target protons in the wall to produce the gamma-rays. The present finding allows us to estimate the total CR proton energy to be similar to 10(48) erg, 0.1% of the total energy of the SN explosion.