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

Area of Science:

• Astrophysics
• Particle Physics
• Cosmic Ray Physics

Background:

• The cosmic-ray spectrum exhibits a
• knee
• around 1 PeV, suggesting the existence of Galactic PeV proton accelerators known as PeVatrons.
• Supernova remnant (SNR) G106.3+2.7 is a leading candidate for a PeVatron.
• Previous observations detected very high energy (0.1–100 TeV) gamma rays from G106.3+2.7, with possible explanations including neutral pion decay or inverse Compton scattering by electrons.

Purpose of the Study:

• To analyze Fermi-LAT gamma-ray data from SNR G106.3+2.7 over 12 years.
• To determine the origin of the observed gamma-ray emissions (hadronic vs. leptonic).
• To investigate the role of SNR G106.3+2.7 in cosmic ray acceleration and its connection to the cosmic-ray knee.

Main Methods:

• Analysis of 12 years of Fermi-LAT (Gamma-ray Space Telescope) data.
• Spectral analysis of gamma-ray data in the GeV-TeV energy range.
• Comparison of the gamma-ray spectrum with radio and X-ray data to differentiate between emission mechanisms.

Main Results:

• The GeV-TeV gamma-ray spectrum from G106.3+2.7 is significantly harder than expected from leptonic processes.
• The required total electron energy differs substantially from radio and X-ray observations, indicating a distinct origin for gamma rays.
• The absence of gamma-ray detection below 10 GeV places constraints on the relativistic electron spectrum.
• A hadronic origin for the observed gamma rays is strongly supported by the data.

Conclusions:

• The findings confirm that SNR G106.3+2.7 is a PeVatron, establishing a connection between PeVatrons and SNRs.
• G106.3+2.7 may be the most prominent member of a newly identified class of SNRs emitting gamma rays peaking at TeV energies.
• This population of SNRs could contribute to the cosmic-ray knee and be detectable by future high-energy gamma-ray observatories.