PITCH-ANGLE DISTRIBUTIONS AND TEMPORAL VARIATIONS OF 0.3-300 keV SOLAR IMPULSIVE ELECTRON EVENTS
We investigate the propagation of {approx}0.3-300 keV electrons in five solar impulsive electron events, observed by the WIND three-dimensional Plasma and Energetic Particle instrument, that have rapid-rise and rapid-decay temporal profiles. In two events, the temporal profiles above 25 keV show a second peak of inward-traveling electrons tens of minutes after the first peak, followed by a third peak due to outward-traveling electrons minutes later-likely due to reflection/scattering first at {approx}0.7-1.7 AU past the Earth, and then in the inner heliosphere inside 1 AU. In the five events, below a transition energy E{sub 0} ({approx}10-40 keV), the pitch-angle distributions are highly anisotropic with a pitch-angle width at half-maximum (PAHM) of <15{sup 0} (unresolved) through the time of the peak; the ratio {Lambda} of the peak flux of scattered (22.{sup 0}5-90{sup 0} relative to the outward direction) to field-aligned scatter-free (0{sup 0}-22.{sup 0}5) electrons is {approx}<0.1. Above E{sub 0}, the PAHM at the flux peak increases with energy up to 85{sup 0} at 300 keV, and {Lambda} also increases with energy up to {approx}0.8 at 300 keV. Thus, low-energy electrons propagated essentially scatter-free through the interplanetary medium, while high-energy electrons experienced pitch-angle scattering, with scattering strength increasing with energy. The transition energy E{sub 0} between the two populations is always such that the electron gyroradius ({rho}{sub e}) is approximately equal to the local thermal proton gyroradius ({rho}{sub Tp}), suggesting that the higher energy electrons were scattered by resonance with turbulent fluctuations at scale {approx}>{rho}{sub Tp} in the solar wind.