Ultrahigh-energy photons up to 1.4 petaelectronvolts from 12 γ-ray Galactic sources

The extension of the cosmic-ray spectrum beyond 1 petaelectronvolt (PeV; 10(15) electronvolts) indicates the existence of the so-called PeVatrons-cosmic-ray factories that accelerate particles to PeV energies. We need to locate and identify such objects to find the origin of Galactic cosmic rays(1). The principal signature of both electron and proton PeVatrons is ultrahigh-energy (exceeding 100 TeV) gamma radiation. Evidence of the presence of a proton PeVatron has been found in the Galactic Centre, according to the detection of a hard-spectrum radiation extending to 0.04 PeV (ref. (2)). Although gamma-rays with energies slightly higher than 0.1 PeV have been reported from a few objects in the Galactic plane(3-6), unbiased identification and in-depth exploration of PeVatrons requires detection of gamma-rays with energies well above 0.1 PeV. Here we report the detection of more than 530 photons at energies above 100 teraelectronvolts and up to 1.4 PeV from 12 ultrahigh-energy gamma-ray sources with a statistical significance greater than seven standard deviations. Despite having several potential counterparts in their proximity, including pulsar wind nebulae, supernova remnants and star-forming regions, the PeVatrons responsible for the ultrahigh-energy gamma-rays have not yet been firmly localized and identified (except for the Crab Nebula), leaving open the origin of these extreme accelerators.

Automated summary

The extension of the cosmic-ray spectrum beyond 1 petaelectronvolt indicates the existence of PeVatrons, cosmic-ray factories that accelerate particles to PeV energies. Detection of ultrahigh-energy gamma radiation is a key signature of PeVatrons, with ongoing efforts to locate and identify these extreme accelerators. Despite detecting high-energy gamma rays from various sources, the exact origin and identity of the PeVatrons responsible for the ultrahigh-energy gamma rays remain unknown.