PeVatron

PeVatron is a term used in high-energy astrophysics to describe a class of astrophysical sources capable of accelerating charged particles, primarily protons and heavier nuclei, to petaelectronvolt energies (10^15 eV) or higher. If such accelerators exist in the Galaxy, they could explain the origin of Galactic cosmic rays up to the knee in the spectrum, at a few PeV. The key observational signature of a PeVatron is very-high-energy gamma-ray emission extending to tens or hundreds of TeV with a spectrum consistent with hadronic processes (pion decay) and not limited by the acceleration mechanism. Neutrinos would provide a complementary, unambiguous signature of hadronic acceleration.

The most plausible PeVatron candidates are young supernova remnants and certain regions such as the Galactic Center where gamma rays extend to very high energies; gamma-ray observations by H.E.S.S., VERITAS, MAGIC, and HAWC have revealed sources with high-energy tails, but a definitive PeVatron has not yet been established. Pulsar wind nebulae are also considered in discussions but are typically leptonic sources rather than hadronic PeV accelerators. Distinguishing hadronic from leptonic gamma rays requires spectral analysis and, where possible, spatial association with dense gas.

Future prospects: The Cherenkov Telescope Array (CTA) and next-generation neutrino and gamma-ray observatories will improve sensitivity at PeV energies and help confirm or refute PeVatrons.