Potential PeVatron supernova remnant G106.3+2.7 seen in the highest-energy gamma rays

Cosmic rays (protons and other atomic nuclei) are believed to gain energies of petaelectronvolts (PeV) and beyond at astrophysical particle accelerators called ‘PeVatrons’ inside our Galaxy. Although a characteristic feature of a PeVatron is expected to be a hard gamma-ray energy spectrum that extends beyond 100 teraelectronvolts (TeV) without a cut-off, none of the currently known sources exhibit such a spectrum owing to the low maximum energy of accelerated cosmic rays or owing to insufficient detector sensitivity around 100 TeV. Here, we report the observation of gamma-ray emission from the supernova remnant G106.3+2.7 (refs. 1 , 2 ) above 10 TeV. This work provides flux data points up to and above 100 TeV and indicates that the very-high-energy gamma-ray emission above 10 TeV is well correlated with a molecular cloud 3 rather than with the pulsar PSR J2229+6114 (refs. 4 – 8 ). Regarding the gamma-ray emission mechanism of G106.3+2.7, this morphological feature appears to favour a hadronic origin via the π 0 decay caused by accelerated relativistic protons 9 over a leptonic origin via the inverse Compton scattering by relativistic electrons 10 , 11 . Furthermore, we point out that an X-ray flux upper limit on the synchrotron spectrum would provide important information to firmly establish the hadronic scenario as the mechanism of particle acceleration at the source. Gamma-ray emission up to and above 100 TeV is detected from the supernova remnant G106.3+2.7. The emission above 10 TeV is associated with a molecular cloud rather than the pulsar PSR J2229+6114, favouring a hadronic origin via the π 0 decay caused by accelerated relativistic protons.