New local interstellar spectra for protons, Helium and Carbon derived from PAMELA and Voyager 1 observations

TL;DR

This paper derives new local interstellar spectra for protons, Helium, and Carbon using Voyager 1 and PAMELA data, improving models for cosmic ray propagation at low and high energies.

Contribution

It introduces updated interstellar spectra for key cosmic ray nuclei by fitting galactic propagation models to Voyager 1 and PAMELA observations.

Findings

New spectra cover 3 MeV/nuc to 100 GeV/nuc energy range.

Spectra successfully reproduce Voyager 1 and PAMELA data.

Provides expressions useful for solar modulation studies.

Abstract

With the cosmic ray observations made by the Voyager 1 spacecraft outside the dominant modulating influence of the heliosphere, the comparison of computed galactic spectra with experimental data at lower energies is finally possible. Spectra for specifically protons, Helium and Carbon nuclei, computed by galactic propagation models, can now be compared with observations at low energies from Voyager 1 and at high energies from the PAMELA space detector at Earth. We set out to reproduce the Voyager 1 observations in the energy range of 6 MeV/nuc to 60 MeV/nuc, and the PAMELA spectrum above 50 GeV/nuc, using the GALPROP code, similarly to our previous study for Voyager 1 electrons. By varying the galactic diffusion parameters in the GALPROP plain diffusion model, specifically the rigidity dependence of spatial diffusion, and then including reacceleration, we compute spectra simultaneously for galactic protons, Helium and Carbon.We present new local interstellar spectra, with expressions for the energy range of 3 MeV/nuc to 100 GeV/nuc, which should be of value for solar modulation modeling.