Calculations of the Propagated LIS Electron Spectrum Which Describe the Cosmic Ray Electron Spectrum below ~100 MeV Measured Beyond 122 AU at Voyager 1 and its Relationship to the PAMELA Electron Spectrum above 200 MeV

Abstract: The new Voyager measurements of cosmic ray electrons between 6-60 MeV beyond 122 AU are very sensitive indicators of cosmic ray propagation and acceleration in the galaxy at a very low modulation level. Using a Monte Carlo diffusion model with a source spectrum with a single spectral index of -2.2 at all energies we are able to fit this observed Voyager spectrum and the contemporary PAMELA electron spectrum over an energy range from 6 MeV to ~200 GeV. This spectrum has a break in it but this break is due to propagation effects, not changes in the primary spectrum. This break is gradual, starting at > 2 GeV where the spectrum is ~E^-3.2 and continuing down to ~100 MeV or below where the spectrum becomes ~E^-1.5. At the higher energies the loss terms due to synchrotron radiation and inverse Compton effects which are ~E^2.0 steepen the exponent of the source spectrum by 1.0. At lower energies, these terms become unimportant and the loss is governed by diffusion and escape from the galaxy. A diffusion term which is proportional to beta^-1 below ~0.32 GV (which also fit the H and He spectra measured at Voyager) and has a value = 3x1028 cm^2 x s^-1 at 1 GV and a boundary at +/-1 Kpc will fit the Voyager or other similar spectra at low energies.