The Formation of Galactic Cosmic Rays Spectrum

Abstract

The cosmic ray spectrum can be formed in source by an acceleration process or by the effects of propagation in photons and magnetic fields of galactic and/or extragalactic space. The influence of magnetic field turbulence on the propagation of cosmic ray nuclei has been investigated. We have found that the regular component of galactic magnetic field should be equal to (0.35 μ G) but turbulent component have a mean strange value (4.65 μ G) for description whole feature observed in spectrum of cosmic rays. The propagation paths of nuclei in the galactic magnetic field are changed at the same energies where Extensive Air Shower (EAS) experiments observes alteration in the energy spectrum of cosmic ray. The ‘knee’ in the energy spectrum is due to two processes photo disintegration of nuclei in a soft photon field, type thermal bremsstrahlung with (kT=20) eV and leakage from Galaxy. A concave down among (2 ÷ 5 · 1018) eV observed in the energy spectrum is caused because above this energy the trajectories of protons are strike line in galactic magnetic field, so the propagation length is simple geometric path and do not depend from energy. The trajectories of iron are bending by magnetic field up to energy (1020) eV suffering the photo disintegration, so the secondary protons from destruction of heavy nuclei are isotropic. Only neutrons super high energy can provide some anisotropy. A good agreement with total cosmic ray spectrum can be obtained for parameters widely accepted for the galactic space. The model explain the data set, that the fraction of heavy nuclei increases up to (1016) eV. At energies (1016 ÷ 3 · 1018) eV the mixed mass compositions do not varies so much, but above this energy mass composition become lighter due to photo disintegration process of heavy nuclei. The secondary protons and spectra of light nuclei originating from the destruction of heavy nuclei have the maximum just above the ‘knee’. We suggest that secondary protons (PS) and nuclei of groups (He and CNO) make up the second component of cosmic ray spectrum proposed recently by Wdowczyk (1984), Wdowczyk and Wolfendale (1989), Fichtel and Linsley (1986), and discussed by Gaisser (1991). Verification of the proposed model by the observations of UHE neutrons and VHE/UHE gamma rays from point sources is possible.