The injection of ten electron/$^{3}$He-rich SEP events

TL;DR

This study analyzes ten electron/$^{3}$He-rich solar energetic particle events, revealing injection timings, durations, and associations with coronal mass ejections and radio bursts, providing insights into particle acceleration processes.

Contribution

It offers the first detailed timing and association analysis of electron and ion injections in electron/$^{3}$He-rich SEP events, highlighting the role of CMEs and radio bursts.

Findings

High-energy electrons start injection 17 minutes after low-energy electrons.

Most events have fast, narrow west-limb CMEs launching near low-energy electron injection.

Electron spectra show a continuous power law across energies, indicating seed electrons for acceleration.

Abstract

We have derived the particle injections at the Sun for ten good electron/$^{3}$He-rich solar energetic particle (SEP) events, using a 1.2 AU particle path length (suggested by analysis of the velocity dispersion). The inferred solar injections of high-energy ($\sim$10 to 300 keV) electrons and of $\sim$MeV/nucleon ions (carbon and heavier) start with a delay of 17$\pm$3 minutes and 75$\pm$14 minutes, respectively, after the injection of low-energy ($\sim$0.4 to 9 keV) electrons. The injection duration (averaged over energy) ranges from $\sim$200 to 550 minutes for ions, from $\sim$90 to 160 minutes for low-energy electrons, and from $\sim$10 to 30 minutes for high-energy electrons. Most of the selected events have no reported H$\alpha$ flares or GOES SXR bursts, but all have type III radio bursts that typically start after the onset of a low-energy electron injection. All nine events with SOHO/LASCO coverage have a relatively fast ($>$570km/s), mostly narrow ($\lesssim$30$^{\circ}$), west-limb coronal mass ejection (CME) that launches near the start of the low-energy electron injection, and reaches an average altitude of $\sim$1.0 and 4.7 $R_{S}$, respectively, at the start of the high-energy electron injection and of the ion injection. The electron energy spectra show a continuous power law extending across the transition from low to high energies, suggesting that the low-energy electron injection may provide seed electrons for the delayed high-energy electron acceleration. The delayed ion injections and high ionization states may suggest an ion acceleration along the lower altitude flanks, rather than at the nose of the CMEs.