FLARE VERSUS SHOCK ACCELERATION OF HIGH-ENERGY PROTONS IN SOLAR ENERGETIC PARTICLE EVENTS

Recent studies have presented evidence for a significant to dominant role for a flare-resident acceleration process for high-energy protons in large (gradual) solar energetic particle (SEP) events, contrary to the more generally held view that such protons are primarily accelerated at shock waves driven by coronal mass ejections (CMEs). The new support for this flare-centric view is provided by correlations between the sizes of X-ray and/ or microwave bursts and associated SEP events. For one such study that considered > 100 MeV proton events, we present evidence based on CME speeds and widths, shock associations, and electron-to-proton ratios that indicates that events omitted from that investigation's analysis should have been included. Inclusion of these outlying events reverses the study's qualitative result and supports shock acceleration of > 100 MeV protons. Examination of the ratios of 0.5 MeV electron intensities to > 100 MeV proton intensities for the Grechnev et al. event sample provides additional support for shock acceleration of high-energy protons. Simply scaling up a classic impulsive SEP event to produce a large > 100 MeV proton event implies the existence of prompt 0.5 MeV electron events that are approximately two orders of magnitude larger than are observed. While classic impulsive SEP events attributed to flares have high electron-to-proton ratios ((Sic) 5. x 10(5)) due to a near absence of > 100 MeV protons, large poorly connected (>= W120) gradual SEP events, attributed to widespread shock acceleration, have electron-to-proton ratios of similar to 2 x 10(3), similar to those of comparably sized well-connected (W20-W90) SEP events.