Sizes and shapes of sources in solar metric radio bursts

TL;DR

This study provides the first detailed multi-frequency analysis of solar radio source sizes and shapes using LOFAR, revealing smaller, more elliptical sources that align with scattering models, thus advancing understanding of coronal plasma turbulence.

Contribution

It introduces a novel empirical method for correcting instrumental and ionospheric effects, enabling more accurate size and shape measurements of solar radio sources across frequencies.

Findings

Deconvolved source sizes are smaller than previous estimates.

Sources often exhibit higher ellipticity than previously observed.

Size and shape variations support anisotropic scattering models.

Abstract

Metric and decametric radio-emissions from the Sun are the only direct source of information about the dynamics of non-thermal electrons in the upper corona. In addition, the combination of spectral and imaging (sizes, shapes, and positions) observations of low-frequency radio sources can be used as a unique diagnostic tool to probe plasma turbulence in the solar corona and inner heliosphere. The geometry of the low-frequency sources and its variation with frequency are still not understood, primarily due to the relatively low spatial resolution available for solar observations. Here we report the first detailed multi-frequency analysis of the sizes of solar radio sources observed by the Low-Frequency Array (LOFAR). Furthermore, we investigate the source shapes by approximating the derived intensity distributions using 2D Gaussian profiles with elliptical half-maximum contours. These measurements have been made possible by a novel empirical method for evaluating the instrumental and ionospheric effects on radio maps based on known source observations. The obtained deconvolved sizes of the sources are found to be smaller than previous estimations, and often show higher ellipticity. The sizes and ellipticities of the sources inferred using 2D Gaussian approximation, and their variation with frequency are consistent with models of anisotropic radio-wave scattering in the solar corona.