# The Important Role of Cosmic-Ray Re-Acceleration

## TL;DR

This paper emphasizes the crucial role of cosmic-ray re-acceleration in the galaxy, especially in middle-aged supernova remnants and stellar wind shocks, supported by recent gamma-ray observations.

## Contribution

It highlights the significance of pre-existing cosmic-ray re-acceleration, a factor often overlooked, in explaining cosmic ray energization in astrophysical shocks.

## Key findings

- Re-acceleration plays a fundamental role in cosmic ray energization.
- Gamma-ray observations support the importance of re-acceleration.
- Re-acceleration is significant in supernova remnants and stellar wind shocks.

## Abstract

In the last decades, the improvement of high energy instruments has enabled a deeper understanding of the Cosmic Ray origin issue. In particular, the gamma-ray satellites AGILE (Astrorivelatore Gamma ad Immagini LEggero) and Fermi-LAT (Fermi-Large Area Telescope) have strongly contributed to the confirmation of direct involvement of Supernova Remnants in Cosmic Ray energization. Despite several attempts to fit experimental data assuming the presence of freshly accelerated particles, the scientific community is now aware that the role of pre-existing Cosmic Ray re-acceleration cannot be neglected. In this work, we highlight the importance of pre-existing Cosmic Ray re-acceleration in the Galaxy showing its fundamental contribution in middle aged Supernova Remnant shocks and in the forward shock of stellar winds.