Element Abundances in Impulsive Solar Energetic-Particle Events

TL;DR

This paper investigates element abundances in impulsive solar energetic-particle events, revealing insights into their origin, acceleration processes, and source temperatures through analysis of element enhancement patterns.

Contribution

It introduces a method to determine coronal source temperatures from element enhancement power-laws and links impulsive SEPs to magnetic reconnection in solar jets.

Findings

Element enhancements follow power-laws in A/Q up to Pb.

No evidence of heating suggests early, rapid reconnection and ion acceleration.

Reacceleration by shock waves associated with CMEs may occur in stronger jets.

Abstract

Impulsive solar energetic-particle (SEP) events were first distinguished as the streaming electrons that produce type III radio bursts as distinct from shock-induced type II bursts. They were then observed as the surprisingly-enhanced 3He-rich SEP events, which were also found to have element enhancements rising smoothly with the mass-to-charge ratio A/Q through the elements, even up to Pb. These impulsive SEPs have been found to originate during magnetic reconnection in solar jets where open magnetic field lines allow energetic particles to escape. In contrast, impulsive solar flares are produced when similar reconnection involves closed field lines where energetic ions are trapped on closed loops and dissipate their energy as X-rays, {\gamma}-rays, and heat. Abundance enhancements that are power-laws in A/Q can be used to determine Q values and hence the coronal source temperature in the events. Results show no evidence of heating, implying reconnection and ion acceleration occur early, rapidly, and at low density. Proton and He excesses that contribute their own power-law may identify events with reacceleration of SEPs by shock waves driven by accompanying fast, narrow coronal mass ejections (CMEs) in many of the stronger jets.