Solar Eruptive Phenomena Associated with Solar Energetic Electron Spectral Types

Abstract

The energy spectral shape of solar energetic electron events carries important information on the energetic electron source/acceleration at the Sun. We investigate the association of six newly identified solar energetic electron spectral types with solar eruptive phenomena, including the downward double-power-law (DDPL) spectrum with break energy E _B above 20 keV (DDPL ${}_{{E}_{B}\geqslant 20\mathrm{keV}}$ ), DDPL with E _B below 20 keV (DDPL ${}_{{E}_{B}\lt 20\mathrm{keV}}$ ), upward double-power law (UDPL), single-power-law (SPL), Ellision–Ramaty–like (ER), and logarithmic-parabola (LP). We find that the SPL type shows (the other five types show) an association with hard X-ray flares of ∼38% (∼55%–82%) and an association with west-limb coronal mass ejections (CMEs) of ∼76% (∼85%–93%). Among the other five types, the DDPL ${}_{{E}_{B}\lt 20\mathrm{keV}}$ and ER (LP and DDPL ${}_{{E}_{B}\geqslant 20{\rm{keV}}}$ ) types only have an association with type II radio bursts of ∼7%–8% (∼16%–20%) and an association with halo CMEs of ∼5%–9% (∼11%–21%); however, the UDPL type exhibits a significant (∼47% and ∼50%) association with type II bursts and halo CMEs, with a significantly faster median CME speed of ${1000}_{-120}^{+550}$ km s ^−1 . For DDPL ${}_{{E}_{B}\geqslant 20\mathrm{keV}}$ (DDPL ${}_{{E}_{B}\lt 20\mathrm{keV}}$ ) with a positive (no) correlation between spectral indexes and no (a positive) correlation between the spectral index and break energy, the spectrum appears to be flatter as the associated CME (flare) becomes faster (stronger). These results suggest that the SPL type can result from the initial acceleration process that likely occurs high in the corona, and then provide seed populations for further acceleration processes to form the other five types: the DDPL ${}_{{E}_{B}\lt 20\mathrm{keV}}$ and ER types via flare-related processes, the LP and DDPL ${}_{{E}_{B}\geqslant 20\mathrm{keV}}$ types via CME-related processes, and the UDPL type via CME-driven shocks.

Keywords

• Solar energetic particles
• Solar particle emission
• Solar activity