Coronal Sources of Impulsive Fe-Rich Solar Energetic Particle Events

TL;DR

This paper reviews 111 impulsive Fe-rich solar energetic particle events, analyzing their elemental abundances, associations with solar phenomena, and potential acceleration mechanisms, highlighting the role of coronal plasma conditions and magnetic reconnection.

Contribution

It provides a comprehensive analysis of Fe-rich SEP events, linking elemental abundance patterns to coronal plasma temperatures and reconnection processes, and discusses their solar source regions.

Findings

Fe abundance enhancements scale with (A/Q)^α, with α between 2 and 8.

Most Fe-rich events are associated with both flares and CMEs, especially smaller ones.

Coronal plasma temperatures of 2.5–3.2 MK are key to understanding these events.

Abstract

We review recent work on 111 Fe-rich impulsive solar energetic ($\sim$ 3 MeV/nuc) particle (SEP) events observed from 1994 to 2013. Strong elemental abundance enhancements scale with A/Q, the ion mass-to-charge ratio, as (A/Q)$^{\alpha}$, where 2 $< \alpha <$ 8 for different events. Most Fe-rich events are associated with both flares and coronal mass ejections (CMEs), and those with larger $\alpha$ are associated with smaller flares, slower and narrower CMEs, and lower SEP event fluences. The narrow equilibrium temperature range required to fit the observed A/Q enhancements is 2.5--3.2 MK, far below the characteristic flare temperatures of $>$ 10 MK. Only a small number of SEP events slightly outside this temperature range were found in an expanded search of impulsive Fe-rich events. Event characteristics are similar for events isolated in time and those occurring in clusters. The current challenge is to determine the solar sources of the Fe-rich events. Ambient coronal regions in the 2.5--3.2 MK range are broadly distributed both in and outside active regions. We explore the possibility of acceleration from thermal plasmas at reconnecting current sheets in the context of observed standard and blowout jets. Recent current sheet reconnection modelling provides a basis for the A/Q enhancements.