Possible hadronic origin of TeV photon emission from SNR G106.3+2.7

¹ Yunnan Observatories, Chinese Academy of Sciences, Kunming 650011, PR China
e-mail: chyy@ynao.ac.cn
² Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210034, PR China
³ Department of Astronomy, Key Laboratory of Astroparticle Physics of Yunnan Province, Yunnan University, Kunming 650091, PR China
⁴ Key Laboratory of Statistical Modeling and Data Analysis of Yunnan Province, Yunnan University, Kunming 650091, PR China
e-mail: lizhang@ynu.edu.cn

Received: 23 July 2021
Accepted: 9 December 2021

Abstract

Context. Recently, HAWC, ASγ, and LHAASO experiments have reported the gamma-ray spectrum of supernova remnant (SNR) G106.3+2.7 above 40 TeV, indicating that SNR G106.3+2.7 is a promising PeVatron candidate. However, the origin of the gamma-ray spectrum is still debated. Thus, a dedicated theoretical model with self-consistent descriptions is required to decipher the properties of the gamma-ray spectrum for this specific source.

Aims. We construct a theoretical model to explain the multiband photon emission from the PeVatron SNR G106.3+2.7.

Methods. In our model, the acceleration and propagation of particles from the Bohm-like diffusion region inside the SNR to the Galactic diffusion region outside the SNR are described through nonlinear diffusive shock acceleration (NLDSA). The main content of our NLDSA model is solving the hydrodynamic equations numerically for gas density, gas velocity, and gas pressure and the equation for the quasi-isotropic particle momentum distribution. The consequent multiband nonthermal emission stems from two different regions, namely the acceleration region and the escaping region.

Results. Our model is capable of explaining the multiband photon emission via the dominant synchrotron radiation of the electrons accelerated inside the SNR. The photons with energy of ≳GeV are naturally produced by the protons inside and outside the SNR. Moreover, photons in the energy range of ~1−~ 100 TeV are due to the interaction of escaped protons with dense molecular clouds.

Conclusions. For photons with energy E_γ ≳ 1 GeV from SNR G106.3+2.7, our results here favor a hadronic origin, where the photons in the energy range of ~1G eV to ~1 TeV are produced inside the SNR through proton-proton interaction, while photons with E_γ ≳ 1 TeV originate from the interaction of escaped protons with a dense molecular cloud.