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Description
Since 2012 August Voyager 1 has been observing the local interstellar energy spectra of Galactic cosmic-ray nuclei down to 3MeV/nuc and electrons down to 2.7MeV. The H and He spectra have the same energy dependence between 3 and 346MeV/nuc, with a broad maximum in the 10-50MeV/nuc range and a H/He ratio of 12.2+/-0.9. The peak H intensity is ~15 times that observed at 1AU, and the observed local interstellar gradient of 3-346MeV H is -0.009+/-0.055%/AU, consistent with models having no local interstellar gradient. The energy spectrum of electrons (e^-^+e^+^) with 2.7-74MeV is consistent with E^-1.30+/-0.05^ and exceeds the H intensity at energies below ~50MeV. Propagation model fits to the observed spectra indicate that the energy density of cosmic-ray nuclei with >3MeV/nuc and electrons with >3MeV is 0.83-1.02eV/cm^3^ and the ionization rate of atomic H is in the range of 1.51-1.64x10^-17^s^-1^. This rate is a factor >10 lower than the ionization rate in diffuse interstellar clouds, suggesting significant spatial inhomogeneity in low-energy cosmic rays or the presence of a suprathermal tail on the energy spectrum at much lower energies. The propagation model fits also provide improved estimates of the elemental abundances in the source of Galactic cosmic rays.
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