# Interaction between Molecular Clouds and MeV-TeV Cosmic-ray Protons Escaped from Supernova Remnants

## TL;DR

This paper presents a model explaining how MeV and GeV-TeV cosmic-ray protons interact with molecular clouds around supernova remnants, accounting for observed iron line emissions and gamma-ray spectra, supporting a hadronic origin.

## Contribution

The study introduces an analytical model linking MeV and GeV-TeV cosmic-ray behaviors with observed emissions around supernova remnants, highlighting the role of CR escape and interaction.

## Key findings

- Model reproduces iron line intensities and gamma-ray spectra for W28 and W44.
- Supports hadronic scenario for gamma-ray emissions from SNRs.
- Shows MeV CRs are confined during SNR-cloud collision, then leak into clouds.

## Abstract

Recent discovery of the X-ray neutral iron line (Fe I K\alpha at 6.40 keV) around several supernova remnants (SNRs) show that MeV cosmic-ray (CR) protons are distributed around the SNRs and are interacting with neutral gas there. We propose that these MeV CRs are the ones that have been accelerated at the SNRs together with GeV-TeV CRs. In our analytical model, the MeV CRs are still confined in the SNR when the SNR collides with molecular clouds. After the collision, the MeV CRs leak into the clouds and produce the neutral iron line emissions. On the other hand, GeV-TeV CRs had already escaped from the SNRs and emit gamma-rays through interaction with molecular clouds surrounding the SNRs. We apply this model to the SNRs W28 and W44 and show that it can reproduce the observations of the iron line intensities and the gamma-ray spectra. This can be another support of a hadronic scenario for the gamma-ray emissions from these SNRs.