Species-dependent Variability in the Energy Spectra of Intense Solar Energetic Particle Events Observed by PSP/ISʘIS/EPI-Hi/LET

Solar energetic particle (SEP) events, comprising electrons, protons, and heavy ions with energies ranging from tens of keV nuc⁻¹ to several GeV nuc⁻¹, offer critical insights into solar particle acceleration and transport mechanisms. The Parker Solar Probe Integrated Science Investigation of the Sun High Energy Energetic Particle Instrument (EPI-Hi) has enabled in situ measurements of 16 ion species in the near-Sun environment, including both commonly studied ions (H, He, O, and Fe) and less frequently analyzed species (C, N, Ne, Na, Mg, Al, Si, S, Ar, Ca, Cr, and Ni) at multi-MeV nuc⁻¹ energies. This study presents a comprehensive spectral and compositional analysis of intense SEP events observed by EPI-Hi’s Low Energy Telescope (LET), incorporating newly derived species-specific geometric factors and instrument response variations. Energy spectra are characterized using Band function fits across different intensity phases of each event, accounting for changes in instrument mode, energy coverage, and detection efficiency. Relative contributions of each ion species during the SEP events are also examined. The results reveal a trend of increasing spectral indices with intensity during the 11 studied events, indicating that low-energy particle enhancements dominate during the high-intensity phase. By extending the analysis beyond the commonly studied ion species, this work provides a more complete picture of SEP composition and contributes to a deeper understanding of their source conditions and transport dynamics in the inner heliosphere. Finally, this paper and its appendices document new instrument response functions used for the EPI-Hi/LET public data release going forward.