Coronal Mass Ejections, Shock Waves, and the Acceleration of Solar Energetic Particle Events

Observatoire de Paris, Section de Meudon, DASOP, CNRS-UMR~8645, F-92195 Meudon, France

Energetic particles observed in interplanetary space after flares (SEPs) were long believed to be accelerated together with the interacting particles in the low solar corona. Charge states and the association with coronal mass ejections (CMEs) have more recently led to the view that the longest lasting and most energetic SEPs (``gradual'' SEPs) result from acceleration by the bow shock of the CME.
The bow shock scenario is confronted in this contribution with observations of both interacting electrons in the solar corona and particle time histories measured at 1 AU during a few gradual SEPs. We argue that coronal acceleration processes leave their imprints in the particle time profiles in interplanetary space during one to several hours starting with the flare. The evidence comprises the time-association of enhancements of interplanetary particle fluxes with rises of coronal radio emissions and with structural changes of radio sources not only at the onset (impulsive phase), but also during later phases of the events.
It is concluded that acceleration processes in the low and middle corona, far downstream of the CME, supply both interacting and at least part of the interplanetary particles. The evolution of the radio emission suggests delayed coronal acceleration in a rather tenuous plasma, which is consistent with the low charge states reported during gradual SEPs. We argue that the CME may play the role of a trigger or even contribute to the buildup of magnetic stresses in the corona, but that its bow shock is unlikely the main accelerator of the high-energy particles.