Authors: Abdullah A. Shmies (The University of Texas at San Antonio), Maher A. Dayeh (Southwest Research Institute), Radoslav Bučîk (Southwest Research Institute), Samuel T. Hart (Southwest Research Institute)

Extreme solar energetic particle (SEP) events sometimes show enhancements in Fe and ³He, which are typically abundant in impulsive events. This study investigates whether these enhancements originate from the parent flare associated with the coronal mass ejection (CME) of the event, or from the re-acceleration of residual material from earlier impulsive events. We analyze 39 SEP events from NOAA’s SPE list, which defines an extreme SEP as one where the >10 MeV integrated flux exceeds 10 pfu. To determine solar particle release (SPR) times, we apply velocity dispersion analysis to WIND/LEMT data and compare the results to the onsets of type III radio bursts from WIND/WAVES. Elemental abundance ratios (Fe/O and ³He/⁴He) are derived from ACE/ULEIS and SIS measurements. We find that extreme SEP events with short SPR delays—indicating good magnetic connectivity to the source—are the ones that display ³He and Fe enhancements. Events with delayed SPR times show no such enrichment, suggesting that these enhancements are localized and not distributed uniformly across the CME front. The lack of systematic association with prior impulsive activity rules out re-acceleration of remnant flare material as the dominant cause. This points to localized acceleration processes, possibly including the parent flare or associated jet activity, as the source of enriched composition in well-connected events.