Delay-time Distributions of Solar Energetic Particles

Abstract

We present an analytic model for the intensity-time profile of solar energetic particle events, based on considerations related to the delay-time distribution that results from interplanetary scattering of a focused distribution of energetic particles. For instantaneous injection, the intensity-time profile is shown to be well described by a Lévy distribution at times up to and just past the time of peak intensity. This allows a fitting procedure that uses velocity dispersion analysis of both the onset time and the peak time to estimate the time of particle release, the magnetic connection length, and the scattering length (and its dependence on velocity). Furthermore, the delay-time distribution can be used as a Green function response when taking into account particle injections of finite duration, in order to infer the release time profile in extended events.