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

Abstract

RX J1713.7−3946 is the most remarkable TeV γ-ray SNR which emits γ-rays in the highest energy range. We 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 γ-rays and ISM protons than the H 2 gas alone. In particular, the southeastern rim of the γ-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 comic ray (CR) protons react with ISM protons to produce the γ-rays. This provides another step forward for the hadronic origin of the γ-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 γ-rays. Most of the neutral gas was likely swept up by the stellar wind of an OB star prior to the SNe 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 γ-rays. The present finding allows us to estimate the total CR proton energy to be ∼10 48 ergs, 0.1 % of the total energy of a SNe.

MAGIC reveals a complex morphology within the unidentified gamma-ray source HESS J1857+026

“…We do not, however, exclude a hadronic origin due to the possible presence of cold, dense atomic gas within the proposed 13 CO cavity, which could also act as target material for accelerated hadrons (e.g. see Fukui et al 2012).…”

Prospects for Cherenkov Telescope Array Observations of the Young Supernova Remnant RX J1713.7−3946

“…2. Hadronic component.Based on CO and H I observations, we obtain the total target gas column density (atomic + molecular; Fukui et al 2012) and use it as a template that is assumed to trace the hadronic gamma-ray morphology.…”

“…Different gamma-ray images in the energy range of 1-100TeV are generated by changing A p /A e , the ratio between the hadronic and leptonic contributions. Figures 1(a) and (b) show the images for A p /A e =0.01 (lepton dominated; e.g., Abdo et al 2011) and 100 (hadron dominated; e.g., Fukui et al 2012), respectively. Each image corresponds to 50hr of observations with CTA.…”

The origin of cosmic rays and TeV gamma-ray astronomy

“…It should be stressed that in this leptonic model, about 25% of the shock ram kinetic energy flux goes into the acceleration of protons, while less than 1% into the highenergy electrons. A different and more detailed study of the molecular and atomic gas around RXJ 1713.7-3946 reports the observations of a low-density cavity created by the stellar wind of the progenitor with a surrounding denser wall [25]. The gamma rays are produced by protongas collisions in the dense wall while the low gas densities in the inner part explain the non-observation of thermal Xray emission by Suzaku.…”

“…The gamma rays are produced by protongas collisions in the dense wall while the low gas densities in the inner part explain the non-observation of thermal Xray emission by Suzaku. It is estimated from multi-zone hadronic modeling of RXJ 1713.7-3946 that about 0.1% of the kinetic energy of the SNR is converted into highenergy particles [25]. The future ground-based observatory CTA will have an angular resolution of 1-2 arcminutes.…”