Direct Numerical Simulations of Cosmic-ray Acceleration at Dense Circumstellar Medium: Magnetic Field Amplification by Bell Instability and Maximum Energy

TL;DR

This study uses numerical simulations to demonstrate that supernova shocks in dense stellar winds can accelerate cosmic rays to PeV energies, highlighting the role of magnetic instabilities and wind parameters.

Contribution

It provides a detailed numerical analysis showing how supernova remnants in dense winds can act as PeVatrons, emphasizing the importance of magnetic field amplification and wind properties.

Findings

Supernova shocks in dense winds can reach PeV energies.

Magnetic field amplification via Bell instability is crucial.

High mass-loss rates enhance maximum cosmic-ray energies.

Abstract

Galactic cosmic rays are believed to be accelerated at supernova remnants. However, whether supernova remnants can be Pevatrons 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 which treats cosmic-ray dynamics coupled to magnetohydrodynamics to follow gas dynamics. The fast shock expanding in a dense ionized wind is able to trigger the 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 make the blast wave a Pevatron, 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 $10^{-3}$ Msun yr$^{-1}$. It has been recently invoked 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 Pevatron phase in early times after the shock breakout.