33ND INTERNATIONAL COSMIC RAY CONFERENCE, RIO DE JANEIRO 2013 THE ASTROPARTICLE PHYSICS CONFERENCE Furthering Our Understanding of Wide Longitude He-rich SEP Events

Abstract: With the significant separation betweenACE and the twin STEREO spacecraft solar energetic particle (SEP) events can be observed simultaneously from substantially different longitudinal locations relative to the solar source. One of the surprising results from such multi-spacecraft studies is the observation of He-rich SEP events over a wide longitude range. As these events are generally believed to originate from relatively small solar source regions (e.g., 5-10), it was unexpected to observe them on multiple spacecraft spanning up to 130 of longitude. Although the study of these events is ongoing, it is still not clear how the large longitudinal distribution is created. In an effort to further our understanding of these events, we have used the ACE and STEREO SEP data to identify seven single-spacecraft He-rich events similar in peak intensity to those observed over wide longitudes. Given the absence of detection on two of the three spacecraft, we determined maximum standard deviations for the longitudinal spread of these events and found them to be significantly smaller than those of the multi-spacecraft He-rich events. This indicates that the mechanism responsible for distributing the SEPs in longitude is variable and able to produce longitudinal distributions with a range of widths