Cosmic ray acceleration and escape from supernova remnants

Understand

Galactic cosmic ray (CR) acceleration to the knee in the spectrum at a few PeV is only possible if the magnetic field ahead of a supernova remnant (SNR) shock is strongly amplified by CR escaping the SNR.

• A model formulated in terms of the electric charge carried by escaping CR predicts the maximum CR energy and the energy spectrum of CR released into the surrounding medium.
• We find that historical SNR such as Cas A, Tycho and Kepler may be expanding too slowly to accelerate CR to the knee at the present time.