Origin of the modulation of the radio emission from the solar corona by a fast magnetoacoustic wave

Kolotkov, D. Y., Nakariakov, V. M. and Kontar, E. P. (2018) Origin of the modulation of the radio emission from the solar corona by a fast magnetoacoustic wave. Astrophysical Journal, 861(1), 33. (doi:10.3847/1538-4357/aac77e)

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Observational detection of quasi-periodic drifting fine structures in a type III radio burst associated with a solar flare SOL2015-04-16T11:22, with the LOw Frequency ARray (LOFAR), is presented. Although similar modulations of the type III emission have been observed before and were associated with the plasma density fluctuations, the origin of those fluctuations was unknown. Analysis of the striae of the intensity variation in the dynamic spectrum allowed us to reveal two quasi-oscillatory components. The shorter component has an apparent wavelength of ~2 Mm, phase speed of ~657 km s−1, which gives an oscillation period of ~3 s, and a relative amplitude of ~0.35%. The longer component has a wavelength of ~12 Mm and relative amplitude of ~5.1%. The short frequency range of the detection does not allow us to estimate its phase speed. However, the properties of the shorter oscillatory component allowed us to interpret it as a fast magnetoacoustic wave guided by a plasma nonuniformity along the magnetic field outwards from the Sun. The assumption that the intensity of the radio emission is proportional to the amount of plasma in the emitting volume allowed us to show that the superposition of the plasma density modulation by a fast wave and a longer-wavelength oscillation of an unspecified nature could readily reproduce the fine structure of the observed dynamic spectrum. The observed parameters of the fast wave give an absolute value for the magnetic field in the emitting plasma of ~1.1 G, which is consistent with the radial magnetic field model.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Kontar, Professor Eduard
Authors: Kolotkov, D. Y., Nakariakov, V. M., and Kontar, E. P.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal
Publisher:American Astronomical Society
ISSN (Online):1538-4357
Published Online:28 June 2018
Copyright Holders:Copyright © 2018 The American Astronomical Society
First Published:First published in Astrophysical Journal 861(1): 33
Publisher Policy:Reproduced in accordance with the publisher copyright policy
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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
728901Consolidated Grant in Solar PhysicsLyndsay FletcherScience & Technology Facilities Council (STFC)ST/P000533/1S&E P&A - PHYSICS & ASTRONOMY