Intense Flares Without Solar Energetic Particle Events

We study favorably located (western hemisphere) X-class flares that were not associated with solar energetic particle (SEP) events. Three of the four such flares that occurred during the present cycle lacked coronal mass ejections (CMEs), consistent with the current paradigm. Soft X-ray data for these three events show either outward moving loops above the main flare loop or a much slower rise of the flare loop itself, as predicted in bipolar reconnection models. However, unlike fully eruptive events, the outward moving loops appear to stop at a certain distance. We speculate that they are held back by overlying magnetic field, as implied in soft X-ray images. The flare that was associated with a CME (but not an SEP event) produced metric and decametric type III bursts, but those without CMEs did not. Other characteristics for the flares not associated with SEP events include relatively short decay times of hard X-ray emission at 30--50 keV. We are extending our study to include additional (somewhat smaller) events to try to identify key parameters that keep intense flares from erupting and accompanying SEP events.