Subsecond time evolution of type III solar radio burst sources at fundamental and harmonic frequencies

Chen, X. , Kontar, E. P. , Chrysaphi, N. , Jeffrey, N. L.S. , Gordovskyy, M., Yan, Y. and Tan, B. (2020) Subsecond time evolution of type III solar radio burst sources at fundamental and harmonic frequencies. Astrophysical Journal, 905(1), 43. (doi: 10.3847/1538-4357/abc24e)

Abstract

Recent developments in astronomical radio telescopes opened new opportunities in imaging and spectroscopy of solar radio bursts at subsecond timescales. Imaging in narrow frequency bands has revealed temporal variations in the positions and source sizes that do not fit into the standard picture of type III solar radio bursts, and require a better understanding of radio-wave transport. In this paper, we utilize 3D Monte Carlo ray-tracing simulations that account for the anisotropic density turbulence in the inhomogeneous solar corona to quantitatively explain the image dynamics at the fundamental (near plasma frequency) and harmonic (double) plasma emissions observed at ∼32 MHz. Comparing the simulations with observations, we find that anisotropic scattering from an instantaneous emission point source can account for the observed time profiles, centroid locations, and source sizes of the fundamental component of type III radio bursts (generated where fpe ≈ 32 MHz). The best agreement with observations is achieved when the ratio of the perpendicular to the parallel component of the wavevector of anisotropic density turbulence is around 0.25. Harmonic emission sources observed at the same frequency (∼32 MHz, but generated where fpe ≈ 16 MHz) have apparent sizes comparable to those produced by the fundamental emission, but demonstrate a much slower temporal evolution. The simulations of radio-wave propagation make it possible to quantitatively explain the variations of apparent source sizes and positions at subsecond timescales both for the fundamental and harmonic emissions, and can be used as a diagnostic tool for the plasma turbulence in the upper corona.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Kontar, Professor Eduard and Jeffrey, Dr Natasha and Chrysaphi, Dr Nicolina and Chen, Dr Xingyao
• Authors: Chen, X., Kontar, E. P., Chrysaphi, N., Jeffrey, N. L.S., Gordovskyy, M., Yan, Y., and Tan, B.
• College/School: College of Science and Engineering > School of Physics and Astronomy
• Journal Name: Astrophysical Journal
• Publisher: IOP Publishing
• ISSN: 0004-637X
• ISSN (Online): 1538-4357
• Published Online: 16 October 2020
• Copyright Holders: Copyright © 2020 The Authors
• First Published: First published in Astrophysical Journal 905(1):43
• Publisher Policy: Reproduced under a Creative Commons licence