Solar near-relativistic electrons on 2000 May 1: insights into injection and transport along the interplanetary magnetic field.

Monte-Carlo simulations are employed to study the time-dependent transport of solar energetic particles in the interplanetary medium. By assuming the guiding center approximation, we quantify the competing effects of focusing and pitch-angle scattering on energetic particles propagating along a Parker spiral magnetic field line. The effects of magnetic field fluctuations are modeled by pitch-angle diffusion. In two models, we simulate an isotropic and an anisotropic pitch-angle diffusion. Since we consider that the scattering centers are frozen in the expanding solar wind, we also include both the effects of solar wind convection and adiabatic deceleration. The results of these simulations are pitch-angle distributions and time-intensity profiles that can be compared to the observations when taking into account the angular response of the detector. Comparison of the simulations with near-relativistic (45-312 keV) electron events observed by the Electron, Proton and Alpha Monitor on board the Advanced Composition Explorer provide an estimation of the characteristics of both the injecting source and the properties of the transport in the interplanetary medium. We apply the model to the solar energetic particle event observed on 2000 May 1. This event has been associated with a west narrow fast CME. By analysing X-ray and radio observations we conclude that there are several emission episodes during the event. Therefore, we present a study of the first two hours of the event where we propose two different scenarios: 1) a single time-extended injection from the solar corona and 2) a composite injection (an impulsive plus a time- extended injection). In addition, the long-duration behaviour of the event indicates the presence of yet another, possibly shock associated, injection component. From the simulations, we are able to infer the properties of the transport and constrain the injection of solar energetic electrons in the interplanetary medium.