Onsets and spectra of impulsive solar energetic electron events observed near the Earth

TL;DR

This study models how solar energetic electrons travel through the solar wind, revealing that plasma turbulence and density variations cause spectral features and timing effects observed near Earth, enhancing understanding of solar flare acceleration.

Contribution

The paper introduces a comprehensive simulation of electron transport that accounts for plasma turbulence and inhomogeneity, explaining observed spectral and timing features of impulsive solar energetic electrons.

Findings

Spectral break arises from wave-particle interactions in non-uniform plasma.

Early low-energy electron onsets are due to plasma turbulence effects.

Spectral flattening below the break energy is explained by the model.

Abstract

Impulsive solar energetic electrons are often observed in the interplanetary space near the Earth and have an attractive diagnostic potential for poorly understood solar flare acceleration processes. We investigate the transport of solar flare energetic electrons in the heliospheric plasma to understand the role of transport to the observed onset and spectral properties of the impulsive solar electron events. The propagation of energetic electrons in solar wind plasma is simulated from the acceleration region at the Sun to the Earth, taking into account self-consistent generation and absorption of electrostatic electron plasma (Langmuir) waves, effects of non-uniform plasma, collisions and Landau damping. The simulations suggest that the beam-driven plasma turbulence and the effects of solar wind density inhomogeneity play a crucial role and lead to the appearance of a) spectral break for a single power-law injected electron spectrum, with the spectrum flatter below the break, b) apparent early onset of low-energy electron injection, c) the apparent late maximum of low-energy electron injection. We show that the observed onsets, spectral flattening at low energies, and formation of a break energy at tens of keV is the direct manifestation of wave-particle interactions in non-uniform plasma of a single accelerated electron population with an initial power-law spectrum.