Acceleration of galactic electrons at the solar wind termination shock and Voyager 1 observations

Abstract

Diffusive shock acceleration (DSA) , as an acceleration process for G alactic electrons at the solar wind termination shock (TS) , is investigated with a comprehensive numerical model which incorporates shock - acceleration , particle drift s and other major modulation processes in the heliosphere . It is known from our previous work that the efficiency of DSA depends on the shape of ele ctron spectra incident on the TS, which in turn depends on the spectral shape of the very local interstellar spectrum. Modulation processes also influence the efficiency of DSA . We find that TS accelerated electrons can make contributions throughout the he liosphere to intensity levels , especially at lower energies. A n interesting result is that i ncreases caused by DSA at the TS are comparable in magnitude to electron intensity enhancements observed by Voyager 1 ahead of the TS crossing. T he se intensity incr eases are large enough to account for observed intensity peaks, and thus supports the view that DSA is involved in their production. Additionally, t he energy spectra observed by Voyager 1 throughout the heliosheath are reproduced satisfactorily, as well as the PAMELA spectrum at Earth at higher energies . We also find that an increase in the rigidity dependence of the diffusion coefficients for these low - energy electrons seems required to reproduce the spectral shape of observed modulated spectra in the heliosheath at kinetic energy E < ~ 4 MeV . This is different from inter mediate energies where rigidity independent diffusion explains observations satisfactory