Interferometric Imaging with LOFAR Remote Baselines of the Fine Structures of a Solar Type IIIb Radio Burst

TL;DR

This study used LOFAR's remote baselines to image and analyze the fine structures of a solar Type IIIb radio burst, revealing distinct source motions and sizes for fundamental and harmonic emissions, advancing understanding of solar radio wave propagation.

Contribution

It provides the first detailed imaging and analysis of a solar Type IIIb-III pair using LOFAR's remote baselines, highlighting differences in source motion and size.

Findings

Fundamental emission source displaces at about 4 times the speed of light.

Harmonic emission source moves at less than 0.02c.

Harmonic source size is smaller than previously observed.

Abstract

Context. Solar radio bursts originate mainly from high energy electrons accelerated in solar eruptions like solar flares, jets, and coronal mass ejections. A subcategory of solar radio bursts with short time duration may be used as a proxy to understand the wave generation and propagation within the corona. Aims. Complete case studies of the source size, position and kinematics of short term bursts are very rare due to instrumental limitations. A comprehensive multi-frequency spectroscopic and imaging study was carried out of a clear example of a solar type IIIb-III pair. Methods. In this work, the source of the radio burst was imaged with the interferometric mode, using the remote baselines of the LOw Frequency ARray (LOFAR). A detailed analysis of the fine structures in the spectrum and of the radio source motion with imaging was conducted. Results. The study shows how the fundamental and harmonic components have a significantly different source motion. The apparent source of the fundamental emission at 26.56MHz displaces away from the solar disk center at about 4 times the speed of light, while the apparent source of the harmonic emission at the same frequency shows a speed of < 0.02c. The source size of the harmonic emission, observed in this case, is smaller than that in previous studies, indicating the importance of the use of the remote baselines.