2019ApJ...876...27Y

Supernova remnants (SNRs) are thought to be one of the major acceleration sites of galactic cosmic rays and an important class of objects for high-energy astrophysics. SNRs produce multiwavelength, nonthermal emission via accelerated particles at collisionless shocks generated by the interactions between the SN ejecta and the circumstellar medium (CSM). Although it is expected that the rich diversities observed in supernovae (SNe) and their CSM can result in distinct very high energy (VHE) electromagnetic signals in the SNR phase, there are only a handful of SNRs observed in both GeV and TeV γ-rays so far. A systematic understanding of particle acceleration at SNRs in different ambient environments is therefore limited. Here we explore nonthermal emission from SNRs in various circumstellar environments up to 5000 yr from explosion using hydrodynamical simulations coupled with efficient particle acceleration. We find that time evolution of emission characteristics in the VHE regime is mainly dictated by two factors: the number density of the target particles and the amplified magnetic field in the shocked medium. We also predict that the Cherenkov Telescope Array (CTA) will have sufficient sensitivity to detect VHE γ-rays from most young SNRs at distances <=5.0 kpc. Future SNR observations with CTA will thus be promising for probing the CSM environment of SNe and hence their progenitor properties, including the mass-loss history of massive stars.