Modulation of low-energy cosmic ray electrons in the outer heliosphere

Abstract

A drift-modulation model with a solar wind termination shock (TS), including a jovian electron source, was used to study the effects of this heliospheric shock on electron radial intensity profiles, with emphasis on the outer heliosphere. Electron measurements between 1977 and late 2001 at 4–8 MeV and up to ∼82 AU from the Voyager spacecraft make it possible to compare computations with observations using new diffusion coefficients and a revised local interstellar electron spectrum (LIS). Compatibility between the model and the measurements are produced with the shock radius at ∼90 AU, the shock compression ratio at ∼3, and the outer boundary radius between 120 and 140 AU. The small radial gradients observed for these electrons between 15 and 82 AU can easily be reproduced with the consequence that a considerable amount of modulation must take place in the region between the TS and the modulation boundary, depending on the energies considered and the value of the LIS.