Constraints on the Release History of Solar Energetic Particles by Flux-tube Variations

We present the analysis of a large solar near-relativistic (>50 keV) electron event observed by the Wind spacecraft on 1998 April 20. In-situ data show variations of the local magnetic field direction accompanied by changes in the topology of the observed electron pitch-angle distributions. These suggest changes in the magnetic flux tubes scanned by Wind. Using simulations of the interplanetary particle transport, we model the early rising phase of the electron event, from 10:30 to 11:00 UT, and infer the propagation conditions and the injection history of the first arriving 50-82 keV solar electrons. The results reveal a prompt (<=1 min) release in coincidence with the soft X-ray and type III radio bursts, suggesting that the first arriving electrons were flare-accelerated.