Injection timing of solar impulsive electrons

In this study, we investigate two solar impulsive electron events
(1998 Aug 29 and 2002 Oct 20) with low pre-event background, good count
statistics and the electron energy range from ~0.5 keV to ~200 keV.
We assume triangular injection profiles at the Sun with equal rise and
fall times and scatter-free propagation in the interplanetary medium,
and fit the observed time profiles of electron fluxes at all energies
at 1 AU.  We find that for the 1998 August event and the 2002 October
event, the injection of the >~30keV electrons at the Sun starts with
a median delay of ~16 min and ~40 min after the injection of the <~3keV 
electrons, respectively; the injection durations range from ~15
and 5-25 min for energies above ~ 30keV, to 60-80 min and ~130 min below
~3 keV, respectively.  Furthermore, we examine the width of pitch angle
distributions at half maximum and estimate the propagation effects in the
interplanetary medium.  We find that the low-energy electrons propagate
nearly scatter-free, while the high-energy electrons experience some
energy-dependent scattering.  In the two events, thus, the actual solar
injection lasts for ~1-2 hour for low-energy electrons, while only less
than ~20 min for high-energy electrons.  This suggests that low- and 
high-energy electrons are accelerated by different mechanisms, and that
the low-energy electrons may provide a seed population for the 
acceleration of the high-energy electrons.