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

TL;DR

This paper uses a detailed numerical model to show that diffusive shock acceleration at the solar wind termination shock significantly contributes to galactic electron intensities throughout the heliosphere, aligning well with Voyager 1 observations.

Contribution

It introduces a comprehensive numerical model that incorporates shock acceleration, particle drifts, and modulation processes to explain galactic electron spectra and intensities observed by Voyager 1.

Findings

DSA at the TS contributes to electron intensities across the heliosphere.

Increases in electron intensities due to DSA match Voyager 1 observations.

Reproduces Voyager 1 heliosheath spectra and PAMELA data at Earth.

Abstract

Diffusive shock acceleration (DSA), as an acceleration process for Galactic electrons at the solar wind termination shock (TS), is investigated with a comprehensive numerical model which incorporates shock-acceleration, particle drifts 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 electron 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 heliosphere to intensity levels, especially at lower energies. An interesting result is that increases caused by DSA at the TS are comparable in magnitude to electron intensity enhancements observed by Voyager 1 ahead of the TS crossing. These intensity increases are large enough to account for observed intensity peaks, and thus supports the view that DSA is involved in their production. Additionally, the 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 intermediate energies where rigidity independent diffusion explains observations satisfactory.