Imaging a Large Coronal Loop Using Type U Solar Radio Burst Interferometry

• Published in: The Astrophysical journal Vol. 965; no. 2; pp. 107 - 118
• Main Authors: Zhang, Jinge, Reid, Hamish A. S., Carley, Eoin, Lamy, Laurent, Zucca, Pietro, Zhang, Peijin, Cecconi, Baptiste
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.04.2024; IOP Publishing
• Subjects: Altitude; Centroids; Corona; Coronal loops; Deceleration; Density gradients; Electron beams; Electrons; Field strength; Frequency drift; Imaging techniques; Interferometry; Langmuir waves; LOFAR; Magnetic fields; Magnetic loops; Physical properties; Plasma density; Plasma pressure; Plasma temperature; Radio; Solar corona; Solar coronal loops; Solar coronal radio emission; Solar energetic particles; Solar imagery; Solar particle emission; Solar radio bursts
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ad26fd

Abstract Solar radio U-bursts are generated by electron beams traveling along closed magnetic loops in the solar corona. Low-frequency (<100 MHz) U-bursts serve as powerful diagnostic tools for studying large-sized coronal loops that extend into the middle corona. However, the positive frequency drift component (descending leg) of U-bursts has received less attention in previous studies, as the descending radio flux is weak. In this study, we utilized LOFAR interferometric solar imaging data from a U-burst that has a significant descending leg component, observed between 10 and 90 MHz on 2020 June 5th. By analyzing the radio source centroid positions, we determined the beam velocities and physical parameters of a large coronal magnetic loop that reached just about 1.3 R ⊙ in altitude. At this altitude, we found the plasma temperature to be around 1.1 MK, the plasma pressure around 0.20 mdyn, cm −2 , and the minimum magnetic field strength around 0.07 G. The similarity in physical properties determined from the image suggests a symmetric loop. The average electron beam velocity on the ascending leg was found to be 0.21 c , while it was 0.14 c on the descending leg. This apparent deceleration is attributed to a decrease in the range of electron energies that resonate with Langmuir waves, likely due to the positive background plasma density gradient along the downward loop leg.