Evidence for PeV Proton Acceleration from Fermi-LAT Observations of SNR G106.3+2.7

TL;DR

Analysis of 12 years of Fermi-LAT data provides evidence that SNR G106.3+2.7 accelerates protons to PeV energies, supporting its role as a Galactic PeVatron and linking SNRs to the cosmic-ray knee.

Contribution

First detailed gamma-ray spectral analysis of SNR G106.3+2.7 indicating a hadronic origin, confirming it as a PeVatron candidate and connecting SNRs to cosmic-ray acceleration.

Findings

Gamma-ray spectrum is harder than radio/X-ray spectra.

Supports hadronic origin of gamma rays from G106.3+2.7.

Suggests G106.3+2.7 as a key PeVatron contributing to the cosmic-ray knee.

Abstract

The existence of a "knee" at energy ~1 PeV in the cosmic-ray spectrum suggests the presence of Galactic PeV proton accelerators called "PeVatrons". Supernova Remnant (SNR) G106.3+2.7 is a prime candidate for one of these. The recent detection of very high energy (0.1-100 TeV) gamma rays from G106.3+2.7 may be explained either by the decay of neutral pions or inverse Compton scattering by relativistic electrons. We report an analysis of 12 years of Fermi-LAT gamma-ray data which shows that the GeV-TeV gamma-ray spectrum is much harder and requires a different total electron energy than the radio and X-ray spectra, suggesting it has a distinct, hadronic origin. The non-detection of gamma rays below 10 GeV implies additional constraints on the relativistic electron spectrum. A hadronic interpretation of the observed gamma rays is strongly supported. This observation confirms the long-sought connection between Galactic PeVatrons and SNRs. Moreover, it suggests that G106.3+2.7 could be the brightest member of a new population of SNRs whose gamma-ray energy flux peaks at TeV energies. Such a population may contribute to the cosmic-ray knee and be revealed by future very high energy gamma-ray detectors.