On the Hard Gamma-Ray Spectrum of the Potential PeVatron Supernova Remnant G106.3 + 2.7

The Tibet ASγ experiment has measured a γ-ray flux of supernova remnant G106.3+2.7 of up to 100 TeV, suggesting it is potentially a "PeVatron." Challenges arise when the hadronic scenario requires a hard proton spectrum (with spectral index ≈1.8), while usual observations and numerical simulations prefer a soft proton spectrum (with spectral index ≥2). In this paper, we explore an alternative scenario to explain the γ-ray spectrum of G106.3+2.7 within the current understanding of acceleration and escape processes. We consider that cosmic ray particles are scattered by turbulence driven by Bell instabilities. The resulting hadronic γ-ray spectrum is novel, dominating the contribution to the emission above 10 TeV, and can explain the bizarre broadband spectrum of G106.3+2.7 in combination with leptonic emission from the remnant.