The Hunt for Pevatrons: The Case of Supernova Remnants

TL;DR

This paper reviews the ongoing search for Galactic pevatrons, emphasizing that supernova remnants, though prime candidates, have not yet been confirmed as pevatrons, and highlights recent findings in the field.

Contribution

It provides a concise overview of recent results and challenges in identifying Galactic pevatrons, questioning the traditional association with supernova remnants.

Findings

First pevatron detections were not linked to SNRs

All confirmed SNRs have not been shown as pevatrons

VHE gamma-ray regions unassociated with SNRs suggest other pevatrons

Abstract

The search for Galactic pevatrons is now a well-identified key science project of all instruments operating in the very-high-energy domain. Indeed, in this energy range, the detection of gamma rays clearly indicates that efficient particle acceleration is taking place, and observations can thus help identify which astrophysical sources can energize particles up to the $\sim$PeV range, thus being $pevatrons$. In the search for the origin of Galactic cosmic rays (CRs), the PeV range is an important milestone, since the sources of Galactic CRs are expected to accelerate PeV particles. This is how the central scientific goal that is 'solving the mystery of the origin of CRs' has often been distorted into 'finding (a) pevatron(s)'. Since supernova remnants (SNRs) are often cited as the most likely candidates for the origin of CRs, 'finding (a) pevatron(s)' has often become 'confirming that SNRs are pevatrons'. Pleasingly, the first detection(s) of pevatron(s) were not associated to SNRs. Moreover, all clearly detected SNRs have yet revealed to not be pevatrons, and the detection from VHE gamma rays from regions unassociated with SNRs, are reminding us that other astrophysical sites might well be pevatrons. This short review aims at highlighting a few important results on the search for Galactic pevatrons.