First Detection of sub-PeV Diffuse Gamma Rays from the Galactic Disk: Evidence for Ubiquitous Galactic Cosmic Rays beyond PeV Energies

TL;DR

This paper reports the first detection of diffuse gamma rays in the 100 TeV to 1 PeV range from the Galactic disk, providing evidence for cosmic rays being accelerated beyond PeV energies within our galaxy.

Contribution

It presents the first observation of diffuse gamma rays above 100 TeV in the Galactic disk, supporting the hadronic origin of these rays and indicating cosmic ray acceleration beyond PeV energies.

Findings

Detection of gamma rays above 398 TeV in the Galactic disk

Gamma rays are consistent with hadronic emission from proton interactions

Evidence for cosmic rays accelerated beyond PeV energies

Abstract

We report, for the first time, the long-awaited detection of diffuse gamma rays with energies between 100 TeV and 1 PeV in the Galactic disk. Particularly, all gamma rays above 398 TeV are observed apart from known TeV gamma-ray sources and compatible with expectations from the hadronic emission scenario in which gamma rays originate from the decay of $\pi^0$'s produced through the interaction of protons with the interstellar medium in the Galaxy. This is strong evidence that cosmic rays are accelerated beyond PeV energies in our Galaxy and spread over the Galactic disk.