A Survey of ~38-315 keV Electron Events with Beam-Like Anisotropies.
S.E. Hawkins III, E.C. Roelof, R.E. Gold, D.K. Haggerty, G.C. Ho
The Johns Hopkins University Applied Physics Laboratory
Laurel, Maryland, 20723-6099 (ed.hawkins@jhuapl.edu)
Observations of beam-like solar energetic electron events provide new
insight into acceleration and transport of ~38-315 keV particles from
the solar corona to 1 AU. The EPAM instrument on the ACE spacecraft
provides a unique set of measurements with its magnetically deflected
"pure" electron channels, enabling us to unambiguously discriminate
ions from electrons. With this identification, we can then also
utilize our higher sensitivity "foil" electron spectrometers (which
could respond to ions if they are present). This combination of
"pure" and "foil" electron measurements then uniquely allows us to
construct pitch-angle distributions over nearly a full 180-degree
range. The electron observations used in this study have time
resolution ~1 minute. We report on a survey of energetic electron
events with large anisotropies (max/min sector >5:1). Beam-like
pitch-angle distributions imply nearly scatter-free propagation.
Because these electrons are near-relativistic (beta ~0.4-0.7)
knowledge of the path length back to the Sun should in principle
permit one to compute the release time in the corona to within a few
minutes [Roelof et al., this conference]. Although impulsive
injection corresponds to the most obvious beam events, we often find
periods lasting many hours with nearly constant intensity, implying
constant outflow from the corona with no apparent correlation to
the 1-8 angstrom x-ray emission.