PeVatron candidate SNR G106.3+2.7 in a low-density cavity: a multiwavelength test

In this paper, we constrain the density of the interstellar medium (ISM) around the hadronic PeVatron candidate, supernova remnant (SNR) G106.3+2.7, based on X-ray and gamma-ray observations. The purpose of this investigation is to understand the influence of the gaseous environment on this SNR as a proton PeVatron candidate. By modelling the self-regulated propagation of the cosmic rays (CRs) injected from the SNR, we calculate the gamma-ray emission of CRs via the hadronuclear interactions with the molecular cloud and the ISM, and use the measured gamma-ray flux to constrain the ISM density around the SNR. Our results support the picture that the SNR is expanding into a low-density (0.05 cm(-3)) cavity, enabling the SNR to be a potential proton PeVatron despite that it is presently not in the very early phase.