Solar Origin of 3He-rich Solar Energetic Particle Events

For more than three decades, we have known solar energetic particle (SEP) events that are characterized by enrichment of 3He and heavy ions. In order to understand the phenomenon, we first need to know where these ions come from. It is not straightforward to identify the solar source of the 3He-rich SEP event, since it often leaves electromagnetic signatures too small to be detected as a flare in spatially-integrated GOES X-ray measurements. Another ambiguity arises from the fact that 3He-rich SEP events are more often observed at low energies, meaning large uncertainties in the particle injection time. In this work we concentrate on 3He-rich SEP events whose injection times are relatively well determined by the ULEIS and SIS experiments on ACE. We show the association of these 3He-rich events with type III radio bursts and non- or mildly-relativistic electron events, and with solar flares, jets and CMEs. We compare our results with those in the literature, and also discuss the possible origin of problem events where we fail to find any solar signatures in the corona.