Acceleration of Particles by Oblique Shocks and Cosmic Ray Spectra around the Knee Region

Abstract

We examine the first order Fermi acceleration on the presumption that supernova remnant shocks cross ambient magnetic fields with various angles. These oblique shocks accelerate particles more efficiently than the parallel shocks and elevate the maximum energies achievable by the particles. The primary cosmic ray spectrum is strongly dependent upon these energies. We also consider the dependence of the injection efficiency and of spectral indices on obliquity. When indices and absolute fluxes at $10^{12}$ eV are given for six nuclear groups from balloon-borne data, each energy spectrum develops a smooth rigidity dependent knee structure. The resultant total spectrum also behaves similarly and fits well with ground-based experimental data up to several $10^{17}$ eV. It is shown as well that the chemical composition changes significantly from lighter to heavier nuclei as the energies of particles exceed the knee region. Other predicted curves are compared with the experimental data which they reproduce rather well.