Abstract
Type III solar radio bursts are the Sun’s most intense and frequent nonthermal radio emissions. They involve two critical problems in astrophysics, plasma physics, and space physics: how collective processes produce nonthermal radiation and how magnetic reconnection occurs and changes magnetic energy into kinetic energy. Here magnetic reconnection events are identified definitively in Solar Dynamics Observatory UV-EUV data, with strong upward and downward pairs of jets, current sheets, and cusp-like geometries on top of time-varying magnetic loops, and strong outflows along pairs of open magnetic field lines. Type III bursts imaged by the Murchison Widefield Array and detected by the Learmonth radiospectrograph and STEREO B spacecraft are demonstrated to be in very good temporal and spatial coincidence with specific reconnection events and with bursts of X-rays detected by the RHESSI spacecraft. The reconnection sites are low, near heights of 5–10 Mm. These images and event timings provide the long-desired direct evidence that semi-relativistic electrons energized in magnetic reconnection regions produce type III radio bursts. Not all the observed reconnection events produce X-ray events or coronal or interplanetary type III bursts; thus different special conditions exist for electrons leaving reconnection regions to produce observable radio, EUV, UV, and X-ray bursts.
Highlights
Synchrotron emission from supernovae) but are relatively weak
We demonstrate the occurrence of other reconnection and X-ray events without well-correlated large type IIIs, as well as weak radio emissions at other times; these are interpreted as evidence for special conditions being necessary for the production of observable type III and X-ray emission by reconnection events
The evidence is in the form of images of enhanced 93–1700 Å EUV emissions with pairs of upward- and downward-directed jets, current sheets and cusp-like geometries on top of low-lying magnetic loops, and strong outflow events along open magnetic field lines that occur in pairs and are magnetically connected to the jets and cusp-like regions (Figs 2 and 3 plus, especially, Movies B1, B2 and B3 of Supporting Material B)
Summary
Synchrotron emission from supernovae) but are relatively weak. The brightest radio sources (e.g., the Sun and pulsars) involve collective processes, in which energised plasma particles interact collectively to generate intense plasma waves and radio emission. Fine structures are likely, the combination of these individual regions should lead to two bulk reconnection outflows, one Sunwards and one outwards, and to two pairs of jets of energetic particles, one pair Sunwards towards two magnetic footpoints and one pair outwards along open field lines (Fig. 1c). Yohkoh and Hinode X-ray images[15,16,28,29,30,31] sometimes show large-scale X-ray jets and magnetic field configurations that are interpreted in terms of reconnection, bulk plasma motion (both outwards and Sunwards), and heating in or near the putative reconnection region Neither these nor recent published Solar Dynamics Observatory (SDO)[31,32,33], TRACE34, or Hi-C35 images of reconnection spatially resolve the predicted pair structures and only a few discuss radio events[31,33,34]. Whether the electrons producing the radio and X-ray emissions are the same or different remains unknown[18,19,20,36,37], with further acceleration by parallel electric fields and/or wave-particle interactions possible[36], similar to Earth’s auroral region
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
