Solar sources of impulsive solar energetic particle events and their magnetic field connection to the Earth

This paper investigates the solar origin of impulsive solar energetic particle (SEP) events, often referred to as He-3-rich flares, by attempting to locate the source regions of 117 events as observed at similar to 2-3 MeVamu(-1). Given large uncertainties as to when ions at these energies were injected, we use type III radio bursts that occur within a 5 hr time window preceding the observed ion onset, and search in EUV and X-ray full-disk images for brightenings around the times of the type III bursts. In this way we find the solar sources in 69 events. High cadence EUV images often reveal a jet in the source region shortly after the type III burst. We also study magnetic field connections between the Earth and the solar sources of impulsive SEP events as identified above, combining the potential field source surface (PFSS) model for the coronal field and the Parker spiral for the interplanetary magnetic field. We find open field lines in and around similar to 80% of the source regions. But only in similar to 40% of the cases, can we find field lines that are both close to the source region at the photosphere and to the Parker spiral coordinates at the source surface, suggesting challenges in understanding the Sun-Earth magnetic field with observations available at present and in near future.