PeV cosmic-ray acceleration by younger supernova remnants

Determine whether supernova remnants at evolutionary stages younger than RX J1713.7−3946 could have accelerated a sufficient amount of PeV cosmic rays during their earlier phases to remain consistent with the observed Galactic cosmic-ray spectrum.

Background

The paper concludes that RX J1713.7−3946 is not currently a PeVatron, despite supporting supernova remnants as major Galactic cosmic-ray accelerators. The authors note that younger supernova remnants may be promising PeVatron candidates, but leave unresolved whether their earlier evolutionary phases could have produced enough PeV cosmic rays to account for the observed cosmic-ray spectrum. This question concerns the time-dependent maximum energy and integrated yield of cosmic-ray acceleration in young remnants.

References

The origin of Galactic cosmic rays up to PeV energies remains one of the central open problems in high-energy astrophysics.

— The unidentified PeV source LHAASO J2108+5157: A microquasar remnant?  (2609.18353 - Martí et al., 16 Sep 2026) in Section 1, Introduction

Our study supports the scenario that SNRs are the main acceleration sources of Galactic cosmic rays, although a significant question regarding their maximum achievable energy remains unanswered. This is because RX J1713.7$-$3946 is widely acknowledged to not be a PeVatron, at least at the present epoch \citep{2007A&A...464..235A,2008ApJ...685..988T,2018A&A...612A...6H,2024A&A...965..113I}. While recent theoretical and observational studies suggest that SNRs at even younger stages are promising candidates for PeVatrons \citep{2013MNRAS.435.1174S,2021ApJ...922....7I,2021NatAs...5..460T,2026arXiv260422621C}, further investigation is required to determine whether they could have accelerated a sufficient amount of PeV cosmic rays during their earlier phases to remain consistent with the observed cosmic-ray spectrum.

— Impact of Upstream Clumpiness on Supernova Remnant Forward Shock Evolution in Molecular Cloud Environments  (2608.17477 - Tatsumi et al., 18 Aug 2026) in Section Summary and Conclusions

The origin of Galactic cosmic rays (CRs), particularly those reaching energies up to the knee at a few PeV, remains one of the most fundamental open questions in high-energy astrophysics.

— 1LHAASO J1852+0050u: GeV-100TeV Gamma-ray emission Powered by Star-forming Region?  (2609.09763 - Collaboration, 9 Sep 2026) in Section 1, Introduction