Observations and Fitting of Two Adjacent Impulsive Solar Energetic Electrons Events

Two adjacent impulsive Solar Energetic Electron (SEE) events were observed by WIND/ 3DP on November 15, 2010. The temporal profiles of the two events exhibit different behaviors: Event1 shows a rapid rise and rapid decay temporal profile, while Event2 shows a slow rise and very slow decay temporal profile with a duration 5～17 times longer than the duration of Event1. Based on previous studies, Event2 should have experienced much stronger scattering in the Interplanetary Medium (IPM), compared with Event1. However, the similar strongly anisotropic pitch-angle distributions of the two events observed at 1AU suggest the same weak scattering in the IPM (especially near 1AU). On the other hand, Event2 has harder peak flux versus energy spectrum than Event1. Using the telegraph equation with an isosceles-triangle injection function of time, the solar source and interplanetary propagation of these electrons are investigated and then the electron injection profile at the Sun and the electron mean free path in the IPM are obtained from the best-fit to in-situ observations. In Event1, the solar injection of low-energy (high-energy) electrons starts at 14:14±00:04UT (14:36±00:01UT) and lasts for about 50 minutes (about 7 minutes). In Event2, the solar injection of low-energy (high-energy) electrons starts at 14:34±00:13UT (14:25±00:02UT) and lasts for about 170 minutes (about 90 minutes). For both events, the electron energy spectrum during the electron solar injection does not become harder (continuously) with increasing time, suggesting the absence of electron storage in the corona (after acceleration). The inferred electron mean free path in the IPM is larger than that at 1AU for both events. These results suggest that for the two events, the different energy spectra and temporal profiles observed at 1AU were resulted from the electron acceleration at the Sun, not from the propagation effects in the IPM. By comparing the inferred electron injection times with GOES SXR and SOHO white light observations, these two events are likely associated with a CME.