Solar Energetic Electrons, X‐Rays, and Radio Bursts

Abstract

We review recent results on solar energetic electrons observed in situ near 1 AU, and on the radio and X-ray emission generated by these electrons. Near solar maximum, hundreds of solar impulsive electron events are detected per year by the Wind spacecraft. About ∼10% are prompt events, where the electrons at all energies are injected from the Sun at the time of the solar type III radio burst, but in the rest the injection of tens of keV electrons is delayed by ∼10 minutes. For prompt events with associated flare hard X-ray (HXR) emission, the electron spectrum measured at 1 AU shows a rough correlation with that of the HXR-producing electrons at the Sun, but the correlation does not fit a simple thick or thin target model. Recent analysis of several scatter-free events detected from ∼0.4 to 300 keV show that they involve two separate injections, the low energy, ∼0.4 to ∼10 keV electron injection starts prior to the type III burst, while >13 keV electrons are injected ∼10 minutes afterwards. The electron, radio and in situ plasma wave observations are all consistent with the type III radio emission being produced by ∼0.4 - 10 keV electrons. Finally, RHESSI has detected weak HXR bursts that may be a signature of the type III burst acceleration itself and not associated with flares.