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What Shapes the Energy Spectra of Galactic Cosmic Rays in the Local Interstellar Medium?

A. Cummings, E. Stone, B.C. Heikkila, N. Lal, W.R. Webber

in 35th International Cosmic Ray Conference

Contribution: pdf


The Voyager 1 (V1) energy spectra of cosmic-ray elements in the
local interstellar medium (LISM) and models of interstellar propagation
that fit these data, and which also fit the data taken at 1 AU at
high energies \cite{CuSt16}, show a rollover from a power law at
high energies to a broad peak at lower energies.
We examine one of the GALPROP propagation models to investigate the
roles of different physical processes in the rollover of the He spectrum
at lower energies. We find that within the context of a GALPROP plain diffusion model,
about two thirds of the rollover is due to ionization energy
losses in the interstellar medium. The remaining one third is due to a combination of other effects,
including most significantly the transformation from a rigidity source spectrum
to the typical energy per nucleon spectrum presented by observers.
Lesser in significance are changes in the rigidity dependence of the diffusion
coefficient, changes in the injection spectrum, and nuclear interactions.