Yasuo Fukui (Nagoya University Southern Observatories)

HI gas as a key to test hadronic gamma-rays in young SNRs -- Yasuo Fukui Colloquium

Marsfield Lecture Theatre

Abstract

The origin of the cosmic rays is a longstanding question since the discovery of the cosmic rays by V. Hess in 1912. The most likely acceleration site of the cosmic rays is supernova remnants in the Galaxy, while the site still remains to be established observationally. Recent progress in the gamma-ray observations has opened a unique possibility to explore the cosmic-ray origin because the gamma-rays are produced via interaction of cosmic rays with the ambient interstellar medium and/or low-energy photons. In such efforts, radio studies of the interstellar medium are crucial in quantitative determination of the interaction of the cosmic rays.
In this talk I present the interstellar proton distributions, the major interstellar component, in the three young TeV gamma-ray SNRs, RX J1713.7-3946, RX J0852.0-4622 and HESS J1731-347, by using the HI data obtained with the ATCA/Parkes telescopes and the CO data obtained with the NANTEN2 telescope. The derived total interstellar proton distributions, the sum of the atomic and molecular protons, show a good spatial correspondence with the TeV gamma-ray distribution obtained by the HESS Cerenkov telescope. This finding is consistent with the gamma-ray production by the neutral pion decay following the reaction of cosmic-ray protons with the interstellar protons, and provides a necessary condition for the hadronic origin of the gamma-rays. I will emphasize that the inclusion of the HI is crucial in this comparison because the HI gas with no CO emission acts as the dominant target protons in all the three SNRs.
In the end of this talk, I will discuss that the new-generation gamma-ray telescope CTA will provide more gamma-ray sources at a higher angular resolution, allowing us to firmly establish the origin of the cosmic rays.