Direct Numerical Simulations of Cosmic-ray Acceleration at Dense Circumstellar Medium: Magnetic-field Amplification and Maximum Energy

Abstract

Galactic cosmic rays are believed to be accelerated at supernova remnants. However, whether supernova remnants can be PeV is still very unclear. In this work we argue that PeV cosmic rays can be accelerated during the early phase of a supernova blast-wave expansion in dense red supergiant winds. We solve in spherical geometry a system combining a diffusive–convection equation that treats cosmic-ray dynamics coupled to magnetohydrodynamics to follow gas dynamics. A fast shock expanding in a dense ionized wind is able to trigger fast, non-resonant streaming instability over day timescales and energizes cosmic rays even under the effect of p–p losses. We find that such environments produce PeV blast waves, although the maximum energy depends on various parameters such as the injection rate and mass-loss rate of the winds. Multi-PeV energies can be reached if the progenitor mass-loss rates are of the order of 10 −3 M ⊙ yr −1 . It has been recently proposed that, prior to the explosion, hydrogen-rich massive stars can produce enhanced mass-loss rates. These enhanced rates would then favor the production of a PeV phase in early times after shock breakout.