ICRC2015

First near-relativistic electron spike event observed simultaneously by both STEREO spacecraft

3 Aug 2015, 11:15

15m

Mississippi (World Forum)

Oral contribution SH-EX Parallel SH 04 STEREO

Speaker

Dr Andreas Klassen (University of Kiel)

Description

Solar electron spike events are a special subclass of near-relativistic electron events characterized by their short duration, symmetric time profile and their strongly anisotropic pitch angle distribution. All previous studied spike events until now were observed by a single spacecraft only. We present for the first time measurements of an electron spike event that was observed simultaneously by both closely spaced STEREO spacecraft on May 2, 2014. Thereby the orbital-longitudinal separation angle between STEREO-A (STA) and STEREO-B (STB) was less than 38°. The spikes at STA and STB are characterized by very short durations (FWHM$\leq$ 12 min) and almost symmetric time profiles. They exhibit nearly identical properties in: durations, pitch angle distributions (PADs), energy spectra, and intensities. The spike parent source was situated close to the STA nominal magnetic footpoint and was separated by 48° from STB's footpoint. The intensity distribution and the relative onset timing behaved oppositely to what is expected: STB measured a higher intensity and an earlier spike onset than the better connected STA. We suggest that the spike electrons undergo a substantial non-radial injection into interplanetary space from the parent source, a flaring active region, and propagate in a strong non-radial diverging magnetic field. In addition we show that due to the spike properties it is evident that, irrespective of how the electrons were injected into the IP medium, the en-route particle scattering conditions along the paths to STA and STB were very similar. Obviously both s/c detected different parts of the same short particle beam with an angular extension of at least 38° at 1 AU, comparable with the longitudinal separation between STA and STB.