Secondary Accceleration of Cosmic Rays by Supernova Shocks

Abstract

In the common model supernova shock-acceleration of cosmic rays there are two open questions: 1. where does the high energy cosmic rays below the knee (10$^4-10^6$ Gev) come from, and 2. are cosmic ray accelerated only at their origin or contineuosly during their residence in the Galaxy. We show that $10^15$ eV light nuclei are probably accelerted by associations of supernovae. The ratio of the spectra of secondary to primary cosmic rays would be affected by repeated acceleration (also called reacceleration or secondary acceleration) in the ISM during their propagation in the galaxy. The observed secondary and primary CR spectra are used to constrain the amount of such reacceleration by supernova remnants (SNR). Two cases are considered: weak shocks ($1 3$) of relatively young remnants. It is shown that weak shocks produce more reacceleration than what is permitted in the framework of the standard leaky box (SLB) model, making it inconsistent with dispersed acceleration that should be produced by SNR. If the SLB is modified to allow a moderate amount of RA by week shocks, the RA produced by old SNRs agrees with the rate required to fit the secondary-to primaray cosmic-ray data, making a self consistent picture. Significant reacceleration by strong shocks of young SNRs should lead to flattening of the secondary-to primaray ratio at high energies, near 1TeV/nucleon.