LOFAR observations of radio burst source sizes and scattering in the solar corona

Abstract

Low frequency radio wave scattering and refraction can have a dramatic effect on the observed size and position of radio sources in the solar corona. The scattering and refraction is thought to be due to fluctuations in electron density caused by turbulence. Hence, determining the true radio source size can provide information on the turbulence in coronal plasma. However, the lack of high spatial resolution radio interferometric observations at low frequencies, such as with the LOw Frequency ARray (LOFAR), has made it difficult to determine the true radio source size and level of radio wave scattering. Here we directly fit the visibilities of a LOFAR observation of a Type IIIb radio burst with an elliptical Gaussian to determine its source size and position. This circumvents the need to image the source and then de-convolve LOFAR's point spread function, which can introduce spurious effects to the source size and shape. For a burst at 34.76 MHz, we find full width at half maximum (FWHM) heights along the major and minor axes to be $18.8^{\prime }$ $\pm 0.1^{\prime }$ and $10.2^{\prime }$ $\pm 0.1^{\prime }$, respectively, at a plane of sky heliocentric distance of 1.75 R${}_{\odot }$. Our results suggest that the level of density fluctuations in the solar corona is the main cause of the scattering of radio waves, resulting in large source sizes. However, the magnitude of $\epsilon$ may be smaller than what has been previously derived in observations of radio wave scattering in tied-array images.

arXiv comment6 pages, 3 figures, accepted for publication in Astronomy & Astrophysics

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Cited by in corpus (7)

• An Anisotropic Density Turbulence Model from the Sun to 1 au Derived From Radio Observations
• Imaging-spectroscopy of a band-split type II solar radio burst with the Murchison Widefield Array
• First Results from the REAL-time Transient Acquisition backend (REALTA) at the Irish LOFAR station
• Interferometric imaging of the type IIIb and U radio bursts observed with LOFAR on 22 August 2017
• LOFAR imaging of the solar corona during the 2015 March 20 solar eclipse
• Magnetic Field Geometry and Anisotropic Scattering Effects on Solar Radio Burst Observations
• Sizes and shapes of sources in solar metric radio bursts