On the hard $\gamma$-ray spectrum of the potential PeVatron supernova remnant G106.3+2.7

TL;DR

This paper investigates the gamma-ray spectrum of supernova remnant G106.3+2.7, proposing a new hadronic model involving Bell instability-driven turbulence to explain its PeVatron-like emission up to 100 TeV.

Contribution

It introduces an alternative hadronic scenario with turbulence from Bell instability to account for the hard gamma-ray spectrum of G106.3+2.7.

Findings

The gamma-ray spectrum is dominated by hadronic emission above 10 TeV.

The proposed model explains the broadband spectrum with a combination of hadronic and leptonic processes.

The scenario accommodates the observed hard spectrum without requiring an unusually hard proton spectrum.

Abstract

The Tibet AS$\gamma$ experiment has measured $\gamma$-ray flux of supernova remnant G106.3+2.7 up to 100 TeV, suggesting it {being} potentially a "PeVatron". Challenge arises when the hadronic scenario requires a hard proton spectrum (with spectral index $\approx 1.8$), while {usual observations and numerical simulations prefer} a soft proton spectrum {(with spectral index $\geq 2$)}. In this paper, we explore an alternative scenario to explain the $\gamma$-ray spectrum of G106.3+2.7 within the current understanding of acceleration and escape processes. We consider that the cosmic ray {particles} are scattered by the turbulence driven via Bell instability. The resulting hadronic $\gamma$-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.