A model of particle acceleration to high energies by multiple supernova explosions in OB associations

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Abstract
The possibility of cosmic-ray (CR) acceleration to energies above 109 GeV per nucleus in extended Galactic OB associations is analyzed. A two-stage acceleration mechanism is justified: at the first stage, the acceleration by separate shock fronts from spatially and temporally correlated supernovae explosions takes place, and, at the second stage, the Fermi acceleration by supersonic turbulence in an extended, strongly perturbed region near the OB association takes place. We calculate the CR energy spectrum, the change in CR chemical composition with energy, and the energy dependence of the mean logarithm of atomic mass, ‹lnA›, for the accelerated particles. The calculated values are compared with those observed near the break in the energy spectrum. We estimate the turbulence parameters, which allow the observed features of the energy spectrum and the CR enrichment with heavy elements to be explained.