SPECTRA OF SOLAR IMPULSIVE ELECTRON EVENTS OBSERVED NEAR EARTH

Abstract

A statistical survey of the spectral shapes of 62 solar impulsive electron events detected in the ∼ 1 to 300 keV range near Earth by the three-dimensional Plasma and Energetic Particles experiment on the WIND spacecraft is presented. The electron peak flux spectra generally show a broken power-law dependence with a steepening above ∼ 60 keV. The break in the spectrum is pronounced with averaged power-law indices below and above the break of δlow = 1.9 ± 0.3 and δhigh = 3.6 ± 0.7, respectively, and an averaged ratio δlow/δhigh of 0.54 with a standard deviation of 0.09. Two correlations are found: (1) δlow and δhigh are linearly correlated (correlation coefficient of 0.61), (2) The peak fluxes around the break energy and δlow are anticorrelated (coefficient 0.74), with larger events having flatter spectra below the break. Whether the observed spectral breaks are direct signatures of the solar acceleration processes or whether they are due to transport effects from the Sun to Earth is currently not understood.