# Neutral iron line in the supernova remnant IC 443 and implications for MeV cosmic rays

## TL;DR

This paper reports the discovery of bright Fe I Kα line enhancements in supernova remnant IC 443, suggesting MeV protons leak into molecular clouds, providing insights into cosmic ray acceleration.

## Contribution

It presents the first detection of Fe I Kα line enhancements linked to MeV protons in an SNR, supporting models of multi-energy cosmic ray acceleration.

## Key findings

- Fe I Kα line enhancements are associated with molecular clouds.
- The line's intensity matches theoretical predictions for MeV proton interactions.
- The distribution differs from plasma emission, indicating a different origin.

## Abstract

We report a discovery of bright blob-like enhancements of an Fe I K$\alpha$ line in the northwest and the middle of the supernova remnant (SNR) IC 443. The distribution of the line emission is associated with molecular clouds interacting with the shock front, and is totally different from that of the plasma. The Fe I K$\alpha$ line has a large equivalent width. The most plausible scenario for the origin of the line emission is that the MeV protons accelerated in the shell leak into the molecular clouds and ionize the Fe atoms therein. The observed Fe I K$\alpha$ line intensity is consistent with the prediction of a theoretical model, in which MeV protons are accelerated along with GeV and TeV protons at the SNR.