Propagation and source energy spectra of cosmic ray nuclei at high energies

Abstract

A recent measurement of the TRACER instrument on long-duration balloon has determined the individual energy spectra of the major primary cosmic ray nuclei from oxygen (Z = 8) to iron (Z = 26). The measurements cover a large range of energies and extend to energies beyond 1014 eV. We investigate if the data set can be described by a simple but plausible model for acceleration and propagation of cosmic rays. The model assumes a power-law energy spectrum at the source with a common spectral index α for all nuclear species, and an energy-dependent propagation path length (Λ E -0.6) combined with an energy-independent residual path length Λ0. We find that the data can be fitted with a fairly soft source spectrum (α = 2.3-2.4), and with a residual path length Λ0 as high as 0.3 g cm-2. We discuss this model in the context of other pertinent information, and we determine the relative abundances of the elements at the cosmic ray source. © 2009. The American Astronomical Society.