The solar flare electron number problem - time for a new acceleration scenario?

Lyndsay Fletcher

Department of Physics and Astronomy
University of Glasgow

The impulsive phase of a solar flare marks the epoch of rapid conversion of energy stored in the pre-flare coronal magnetic field. Hard X-ray and white light observations both imply that a substantial fraction of flare energy released is converted to the kinetic energy of mildly-relativistic electrons. This constraint has always been problematic for acceleration models, and is becoming even more challenging, as recent observations imply larger and larger electron energy and number fluxes through the corona. Although there is little doubt that magnetic reconnection is central to the flare process, there are several problems with the picture of an electron beam originating in a coronal acceleration site directly at or near the reconnection region and propagating through the corona to the chromosphere. I will review some of the observations pertinent to the electron number problem, and suggest a possible alternative scenario for acceleration involving the ducting of large-scale Alfvenic perturbations, generated as the reconnected field relaxes, directly to the chromosphere. This provides at least two mechanisms for particle acceleration which relieve some of the pressure on electron numbers.