Unusual Type III Burst Dynamics Produced by Diverging Magnetic Fields

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Introduction

Type III solar radio bursts are widely believed to be caused by electron beams accelerated away from the Sun during solar flares. Fast electrons stimulate oscillations in the ambient plasma, which in turn produce radio emission. This plasma emission occurs at specific frequencies that are proportional to the square root of the ambient electron density. The plasma density in the [https://en.wikipedia.org/wiki/Corona solar corona] generally decreases outwards from the solar surface. The emission frequency is therefore related to the height that corresponds to the requisite background density, and type III bursts are characterized by a rapid drift to lower frequencies as the beams move outward.

Figure 1: Source splitting motion at 108 MHz, beginning at 2015/09/21 05:16:53.70 UT. The dashed line in the left panel denotes the slit used for kinematic analysis (Ref. [1]). The two solid black contours are at 0.010 and 0.015 SFU px^-1, and the values in the lower right of each panel note the integrated flux densities in SFU. The star represents the X-ray flare site, the solid semicircle represents the optical disk, the dotted semicircle represents the Newkirk-model limb at 108 MHz, and the white ellipse represents the synthesized beam (resolution element).

References

[1] "Type III Solar Radio Burst Source Region Splitting Due to a Quasi-Separatrix Layer"

[2] "Tracing Electron Beams in the Sun's Corona with Radio Dynamic Imaging Spectroscopy"