Spectroscopic EUV observations of impulsive solar energetic particle event sources

TL;DR

This study investigates EUV line spectroscopy of a solar flare associated with impulsive energetic particles, revealing localized line broadenings near magnetic reconnection sites but not directly linked to ion acceleration.

Contribution

It provides the first detailed spectroscopic analysis of a 3He-rich flare, highlighting that line broadenings are not directly related to energetic ion production.

Findings

Enhanced line broadenings are localized near magnetic reconnection sites.

Line broadenings are associated with redshifts and surrounding blueshifts.

No direct correlation between line broadening and energetic ion signatures.

Abstract

Context. The remote observations of solar flare ion acceleration are rather limited. There are theoretical predictions for signatures of ion acceleration in EUV line profiles. Previous tests involve observations of flares with no evidence for energetic ions. Aims. We aim to examine a source flare of impulsive (or 3He-rich) solar energetic particle events with EUV line spectroscopy. Methods. We inspect all (90+) reported 3He-rich flares of previous solar cycle 23 and find only four (recurrent) jets in the field of view of SOHO CDS. The jet with the most suitable spatial and temporal coverage is analyzed in detail. Results. Two enhanced (non-thermal) line broadenings are observed in the cooler chromospheric / transition-region lines and they are localized near the site where the closed magnetic loops reconnect with the open magnetic field lines. Both enhanced broadenings are found in the sites with redshifts in the lines, surrounded by the region with blueshifts. One enhanced line broadening is associated with a small flare without energetic particle signatures while another occurs just after the particle acceleration signatures of the main flare terminated. Conclusions. The observed excess broadening appears to be not directly related to the energetic ion production and motions. Further investigations where the critical impulsive phase of the flare is covered are required, ideally with high-resolution spectrometers intentionally pointed to the 3He-rich solar energetic particle source.