@article{Mitchell:2026:1538-4357/ae6589,
author = {Mitchell, DG and Lario, D and Raouafi, NE and Mason, GM and Kouloumvakos, A and Collier, H and Roelof, EC and Berland, G and McComas, DJ and Cohen, CMS and Hill, ME and McNutt, RL and Mostafavi, PS and Kasper, JC and Bale, SD and Pulupa, M and Whittlesey, PL},
doi = {1538-4357/ae6589},
journal = {Astrophysical Journal},
title = {The 3He-rich SEP on Event 2024 April 1 at 27 Solar Radii—Indications of Acceleration by Waves and Implications of Coronal Source Location},
url = {http://dx.doi.org/10.3847/1538-4357/ae6589},
volume = {1003},
year = {2026}
}

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TY  - JOUR
AB  - Parker Solar Probe (PSP) observations of a small dispersive event on 2024 April 1 reveal highly enriched <sup>3</sup>He abundance in the suprathermal energy range (40–250 keV nucleon<sup>−1</sup>). Time dispersion observed in this impulsive solar energetic particle (SEP) event is consistent with an estimated onset time of 22:50 UT on 2024 March 31. The event occurred during an orbital segment as PSP moved from about 27 R<inf>s</inf> to about 29 R<inf>s</inf> while outbound in orbit 19. For this segment of the orbit, PSP’s motion in Carrington coordinates remains within about 1° of the same Carrington longitude. The <sup>3</sup>He content is much larger than the usual SEP abundances, especially in this energy range. Additionally, the <sup>3</sup>He energy spectrum is not power law in shape, unlike the H and <sup>4</sup>He spectra. Heavy ions (O, Fe) are also somewhat enhanced. These compositional signatures suggest that this is an example of resonant wave–particle acceleration, as hypothesized for generating the suprathermal seed particles required to account for the enrichment of various species above solar abundances in shock (or compression) acceleration models of SEP events. Like many previously reported impulsive <sup>3</sup>He-rich events, this event is associated with an energetic electron beam, type III radio emission, and a hard X-ray flare. However, associating the hard X-ray event with this SEP event requires significant (∼60°) prompt longitudinal propagation of energetic particles in the low corona before they access open magnetic flux, complicating its interpretation as part of the source process for this particular event.
AU  - Mitchell,DG
AU  - Lario,D
AU  - Raouafi,NE
AU  - Mason,GM
AU  - Kouloumvakos,A
AU  - Collier,H
AU  - Roelof,EC
AU  - Berland,G
AU  - McComas,DJ
AU  - Cohen,CMS
AU  - Hill,ME
AU  - McNutt,RL
AU  - Mostafavi,PS
AU  - Kasper,JC
AU  - Bale,SD
AU  - Pulupa,M
AU  - Whittlesey,PL
DO  - 1538-4357/ae6589
PY  - 2026///
SN  - 0004-637X
TI  - The 3He-rich SEP on Event 2024 April 1 at 27 Solar Radii—Indications of Acceleration by Waves and Implications of Coronal Source Location
T2  - Astrophysical Journal
UR  - http://dx.doi.org/10.3847/1538-4357/ae6589
VL  - 1003
ER  - 

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