ABSTRACT Since 2012 August Voyager 1 has been observing the local interstellar energy spectra of Galactic cosmic-ray nuclei down to 3 MeV nuc −1 and electrons down to 2.7 MeV. The H and He spectra have the same energy dependence between 3 and 346 MeV nuc −1 , with a broad maximum in the 10–50 MeV nuc −1 range and a H/He ratio of 12.2 ± 0.9. The peak H intensity is ∼15 times that observed at 1 AU, and the observed local interstellar gradient of 3–346 MeV H is −0.009 ± 0.055% AU −1 , consistent with models having no local interstellar gradient. The energy spectrum of electrons ( e − + e + ) with 2.7–74 MeV is consistent with E −1.30±0.05 and exceeds the H intensity at energies below ∼50 MeV. Propagation model fits to the observed spectra indicate that the energy density of cosmic-ray nuclei with &gt;3 MeV nuc −1 and electrons with &gt;3 MeV is 0.83–1.02 eV cm −3 and the ionization rate of atomic H is in the range of 1.51–1.64 × 10 −17 s −1 . This rate is a factor &gt;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.

GALACTIC COSMIC RAYS IN THE LOCAL INTERSTELLAR MEDIUM:VOYAGER 1OBSERVATIONS AND MODEL RESULTS