SPECTRA OF COSMIC-RAY PROTONS AND HELIUM PRODUCED IN SUPERNOVA REMNANTS

Abstract

Data obtained in the ATIC-2 (Advanced Thin Ionization Calorimeter), CREAM\n(Cosmic Ray Energetics and Mass)) and PAMELA (Payload for Antimatter Matter\nExploration and Light-nuclei Astrophysics) experiments suggest that elemental\ninterstellar spectra of cosmic rays below the knee at a few times $10^{6}$ GeV\nare not simple power laws, but they experience hardening at magnetic rigidity\nabove about 240 GV. Another essential feature is the difference between proton\nand Helium energy spectra, so that the He/p ratio increases by more than 50% in\nthe energy range from $10^{2}$ to $10^{4}$ GV. We consider the concavity of\nparticle spectrum resulting from the nonlinear nature of diffusive shock\nacceleration in supernova remnants (SNR) as a possible reason for the observed\nspectrum hardening. Helium-to-proton ratio increasing with energy can be\ninterpreted as a consequence of cosmic ray acceleration by forward and reverse\nshocks in SNRs. The contribution of particles accelerated by reverse shocks\nmakes the concavity of the produced overall cosmic ray spectrum more\npronounced. The spectra of protons and helium nuclei accelerated in SNRs and\nreleased into the interstellar medium are calculated. The derived steady state\ninterstellar spectra are in reasonably good agreement with observations.\n