Acceleration of cosmic rays by young core-collapse supernova remnants

Abstract: Context. Supernova remnants (SNRs) are thought to be the primary candidates for the sources of Galactic cosmic rays. According to the diffusive shock acceleration theory, SNR shocks produce a power-law spectrum with an index of s = 2, perhaps nonlinearly modified to harder spectra at high energy. Observations of SNRs often indicate particle spectra that are softer than that and show features not expected from classical theory. Known drawbacks of the standard approach are the assumption that SNRs evolve in a uniform environment, and that the reverse shock does not accelerate particles. Relaxing these assumptions increases the complexity of the problem, because one needs reliable hydrodynamical data for the plasma flow as well as good estimates for the magnetic field (MF) at the reverse shock. Aims. We show that these two factors are especially important when modeling young core-collapse SNRs that evolve in a complicated circumstellar medium shaped by the winds of progenitor stars. Methods. We used high-resolution numerical simulations for the hydrodynamical evolution of the SNR. Instead of parametrizations of the MF profiles inside the SNR, we followed the advection of the frozen-in MF inside the SNR, and thus obtained the B-field value at all locations, in particular at the reverse shock. To model cosmic-ray acceleration we solved the cosmic-ray transport equation in test-particle approximation. Results. We find that the complex plasma-flow profiles of core-collapse SNRs significantly modify the particle spectra. Additionally, the reverse shock strongly affects the emission spectra and the surface brightness.