Voyager 1 in the Local Interstellar Medium: Cosmic-ray Energy Density and Ionization Rate

Abstract:

We present the energy spectra of cosmic ay nuclei and electrons in the local interstellar medium (LISM) from the Cosmic Ray Subsystem on Voyager 1 (V1). We use four models of the local interstellar spectra of nuclei and one of electrons that are constrained by the observations to compute the energy density and ionization rate of atomic H in the LISM above 3 MeV for electrons and protons and above 3 MeV/nuc for nuclei with Z > 1. We find that the total cosmic-ray energy density is in the range 0.82-0.97 eV/cm³, which includes a contribution of 0.023 eV/cm³ from electrons. We find the cosmic-ray ionization rate of atomic H to be in the range 1.45-1.58 x 10^-17 s^-1, which is a factor of more than 10 below the cosmic-ray ionization rate in diffuse interstellar clouds based on astrochemistry methods. We discuss possible reasons for this difference.

Voyager data analysis is supported by NASA Grant NNN12AA012. GALPROP development is supported by NASA Grants NNX13AC47G and NNX10AE78G.