Molecular and atomic gas in the young TeV \gamma-ray SNRs RX J1713.7-3946 and RX J0852.0-4622; evidence for the hadronic production of \gamma-rays

TL;DR

This paper investigates the role of molecular and atomic interstellar gas in the production of gamma-rays in young supernova remnants RX J1713.7-3946 and RX J0852.0-4622, providing evidence for hadronic gamma-ray origins.

Contribution

It demonstrates the spatial correlation between gamma-rays and interstellar protons, supporting the hadronic origin hypothesis and highlighting the importance of clumpy ISM distribution.

Findings

Good spatial correspondence between gamma-rays and interstellar protons.

Clumpy ISM distribution is crucial for shock interactions.

Dense atomic gas may account for dark gas in the local ISM.

Abstract

The interstellar molecular clouds are the site of star formation and also the target for the cosmic ray protons to produce \gamma-rays via the hadronic process. The interstellar atomic gas is enveloping the molecular clouds and may also be dense enough to affect the \gamma-ray production. In this Chapter, some of the basic properties of the interstellar gas both in molecular and atomic forms will be reviewed. Then, it is presented that two young TeV \gamma-ray SNRs, RX J1713.7-3946 and RX J0852.0-4622, show good spatial correspondence between the \gamma-rays and the interstellar protons. The good spatial correspondence provides a support for the hadronic origin of the \gamma-rays in these SNRs. It is emphasized that both molecular and atomic hydrogen plays a role as targets for cosmic ray (CR) protons. The clumpy distribution of the target interstellar medium (ISM) protons is crucial in the interaction of the supernova shocks with the ISM, whereas models with uniform ISM distribution are not viable. Finally, it is suggested that the dense atomic gas without molecules may occupy the dominant part of the dark gas in the local ISM.