Statistical Study of Release Time and Its Energy Dependence of In Situ Energetic Electrons in Impulsive Solar Flares

Abstract

Using the fraction velocity dispersion analysis method, it has been shown recently that in two impulsive solar energetic electron (SEE) events, the release times of near-relativistic electrons at the Sun for outward-propagating electrons are energy dependent and are delayed compared to those of the downward-propagating electrons. In this work, we perform a statistical study of the release time and its energy dependence of near-relativistic electrons in impulsive SEE events. We use in situ observations from the WIND spacecraft and remote hard X-ray observations from the RHESSI and/or Fermi spacecraft. The difference in the release times between outward electrons and downward electrons for 29 events is obtained. In all events, the release of the outward-propagating electrons is delayed from those precipitating downward. In 26 of the 29 events, the release times of outward-propagating electrons also show clear energy dependence. In 15 of these 26 events, in situ electron data from more than five energy channels were available. The delay time as a function of energy for nine of these can be fitted by a form proposed by G. Li et al. (2021, https://doi.org/10.1029/2021GL095138). The implication of this energy-dependent release on the Magnetohydrodynamics turbulence property at the electron acceleration site is discussed.Key PointsDelay of the release of in situ electrons from hard X-ray generating electrons in impulsive solar energetic particle events is examined for 29 eventsClear delays are seen in all events and in most events the delay is energy dependentThe delay shows no energy dependence in fewer than 20% events and the traditional velocity dispersion analysis method only applies in these events