A Timing Study Of Impulsive Solar Energetic Particle Events

The Sun accelerates ions up to tens of GeV and electrons up to hundreds of MeVs in flares and fast coronal mass ejections (CMEs). Solar Energetic Particles (SEPs) are those escaping into the interplanetary medium. SEP events are generally classified into two groups: "Gradual” and "Impulsive", by the duration of the associated soft X-ray burst. Gradual SEP events occur 10/year at solar maximum and they are dominated by protons with large particle intensities. Impulsive SEP events occur 100s /year at solar maximum, and they are dominated by 1-100 keV electrons and MeV/nucleon ion emissions with low particle intensities, enhanced ³He/⁴He ratios up to 10⁴ times coronal and high heavy-ion ionization states. I have made a comprehensive study of impulsive electron events for my PhD. Here, I discuss the temporal relationship between solar impulsive electrons, ions and type III radio emissions for ten nearly scatter-free impulsive events. We find that the low-energy ( 0.4 to 6-9 keV) electron injection starts 9 min before the coronal release of the type III radio burst; the high-energy ( 13 to 300 keV) electron injection starts 8 min after the type III burst; and the injection of MeV/nucleon ions begins 1 hour later. Most of the ten events have no Hα flares or GOES SXR bursts, but all nine events with SOHO/LASCO coronagraph coverage have a rather fast (>570km/s), west-limb CME (6 are < 30° wide) that begins close to the start of low-energy electron injection. These findings suggest that low-energy electron injection provides seed electrons for the delayed high-energy electron injection, and the 1 hour delayed ion injection may be related to acceleration at altitudes > 0.5 -15 R_S.