COMPOSITION AND AZIMUTHAL SPREAD OF SOLAR ENERGETIC PARTICLES FROM IMPULSIVE AND GRADUAL FLARES

We began with a list of 77 flare-associated solar energetic particle (SEP) events observed from 1974 to 1985 by at least one of the two Helios space probes. We classified the SEP parent flares as impulsive (25 cases) or gradual (52 cases) on the basis of their soft X-ray durations. We then compared the intensities of the prompt component of approximately 0.5 MeV electrons, approximately 10 MeV protons, and approximately 10 MeV per nucleon helium for the two classes of SEP flares. We find that SEPs from gradual flares have higher intensities than SEPs from impulsive flares. These differences are most pronounced for protons (about two orders of magnitude) and less for electrons (about one order of magnitude), and helium (about a factor of 5). The SEPs from impulsive flares have a cone of emission" of +/- 50-degrees versus +/- 120-degrees for gradual flares. These results are discussed in the context of recent works on particle acceleration in solar flares.