Properties of Long Duration High-Energy Gamma-Ray Flares

Long duration high-energy gamma-ray flares, recognized the first time in the 1982 June 3 flare, were thought to be rare. However, the Fermi mission with superior gamma-ray sensitivity, has registered almost two dozen such flares. This number allows for investigations into the distribution of the relevant parameters governing these events, in part mitigating some of the observational bias due to instrument sensitivity. We report progress in quantifying key solar parameters that characterize these events. The context for interpreting the gamma-ray data is a stochastic acceleration diffusion model that predicts the precipitation of high-energy ions accelerated in large loops. Two versions of this model are used: a leaky box and one that explicitly includes the spatial diffusion into the denser parts of the solar atmosphere.