Spectroscopic EUV observations of impulsive solar energetic particle event sources

Abstract

Context. Remote observations of solar flare ion acceleration are rather limited. Theoretical predictions for signatures of ion acceleration in extreme ultraviolet (EUV) line profiles have been made. 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 inspected all (more than 90) reported 3He-rich flares of the previous solar cycle 23 and found only 4 (recurrent) jets in the field of view of the Coronal Diagnostic Spectrometer (CDS) on board the Solar and Heliospheric Observatory (SOHO). The jet with the most suitable spatial and temporal coverage was analyzed in detail. Results. Two enhanced (nonthermal) line broadenings are observed in the cooler chromospheric and transition-region lines, and they are localized near the site where the closed magnetic loops reconnect with the open magnetic field lines. The enhanced broadenings are both found at 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 does not appear to be directly related to the energetic ion production and motions. Further investigations are required that cover the critical impulsive phase of the flare, ideally with high-resolution spectrometers that are specifically pointed to the 3He-rich solar energetic particle source.