Evidence for electron excitation of type III radio burst emission

Abstract

Type III radio bursts observed at kilometric wavelengths (~< 0.35 MHz) by the OGO-5 spacecraft are compared with > 45 keV solar electron events observed near I AU by the IMP-5 and Explorer 35 spacecraft for the period March 1968-November 1969 Fifty-six distinct type lI[ bursts extending to ~< 0.35 MHz (> 50 R| equivalent height above the photosphere) were observed above the threshold of the OGO-5 detector; all but two were associated with solar flares. Twenty-six of the bursts were followed ~< 40 min later by > 45 keV solar electron events observed at 1 AU. All of these 26 bursts were identified with flares located west of W09 solar longitude. Of the bursts not associated with electron events only three were identified with flares west of W09, 18 were located east of W09 and 7 occurred during times when electron events would be obscured by high background particle fluxes.Thus almost all type [II bursts from the western half of the solar disk observed by OGO-5 above a detection flux density threshold of the order of 10 -la Wm -z Hz -1 at 0.35 MHz are followed by > 45 keV electrons at 1 AU with a maximum flux of ~> 10 cm -z s -1 ster -1. If particle propagation effects are taken into account it is possible to account for lack of electron events with the type III bursts from flares east of the central meridian. We conclude that streams of ~ 10-100 keV electrons are the exciting agent for type III bursts and that these same electrons escape into the interplanetary medium where they are observed at 1 AU. The total number of > 45 keV electrons emitted in association with a strong kilometer wavelength type III burst is estimated to be >I 5 • 10 a2.

Space Weather: The Solar Perspective

“…Apparently, there is a variety of processes to produce these electrons: 1) The energy spectra extend smoothly to the suprathermal range, down to 2 keV, indicating that these events originate high in the corona (Potter et al, 1980). 2) Electrons accelerated at flare sites with a very wide energy spectrum that cause the radio type III bursts as discussed above (Alvarez et al, 1972). 3) Electrons accelerated at the propagating interplanetary shock waves, both upward and downward, leading to the characteristic "herringbone" pattern of radio spectra shown in Figure 19 .…”

Studies on Plasma and Plasma Waves in the Plasmasphere and Auroral Particle Acceleration Region, by PWS on board the EXOS-D (Akebono) Satellite

“…The observations of the type III radiation using the satellite have been made the start with the ATS-II satellite for the frequency range of 3.0 MHz to 450 kHz (ALEXANDER et al, 1969), then observation study of long wave type HI radio burst has been expanded by using OGO-III (GRAEDEL, 1970), and by Radio Astronomy Explorer (RAE-1) satellite (MOHR et al, 1969;EVANS et al, 1971), OGO-5 and IMP-6 (FRANK and GURNETT, 1972;EvANS et al, 1973;ALVAREZ et al, 1972 andKAISER, 1975). Discussions have been raised for the generation mechanism of type III radio bursts; whether the source is fundamental frequency of the Langmuir waves or the second harmonics of the generated waves, which are formed as the results of the nonlinear coupling processes.…”

Electron Acceleration by Cascading Reconnection in the Solar Corona. Ii. Resistive Electric Field Effects

“…Evenson et al (1984) found that electrons with energies from 5 to 50 MeV in SEP events are always associated with solar flares. Type III radio bursts are also induced by beams of energetic electrons escaping intointerplanetary space from flare sites (e.g., Alvarez et al 1972;Chen & Petrosian 2012). In this study, we investigate acceleration of electrons in a current sheet with cascading reconnection, which may explain hard X-ray (HXR) emissions at flare sites and energetic electrons in SEP events.…”