Interferometric imaging, and beam-formed study of a moving Type IV Radio burst with LOFAR

Abstract

Type IV radio burst has been studied for over 50 years. However, the specifics of the radio emission mechanisms is still an open question. In order to provide more information about the emission mechanisms, we studied a moving type IV radio burst with fine structures (spike group) by using the high resolution capability of Low-Frequency Array (LOFAR) on Aug 25, 2014\textbf{ (SOLA-D-21-00188)}. We present a comparison of Nançay RadioHeliograph (NRH) and the first LOFAR imaging data of type IV radio burst. The degree of circular polarization (DCP) is calculated at frequencies in the range 20$\sim$180 MHz using LOFAR data, and it was found that the value of DCP gradually increased during the event, with values of 10\%$\sim$20\%. LOFAR interferometric data were combined with white light observations in order to track the propagation of this type IV. The kinematics shows a westward motion of the radio sources, slower than the CME leading edge. The dynamic spectrum of LOFAR shows a large number of fine structures with duration of less than 1s and high brightness temperature ($T_{\mathrm{B}}$), i.e. $10^{12}$$\sim$$10^{13}$ K. The gradual increase of DCP supports gyrosynchrotron emission as the most plausible mechanism for the type IV. However, coherent emissions such as Electron Cyclotron Maser (ECM) instability can be responsible for small scale fine structures. Countless fine structures altogether were responsible for such high $T_{\mathrm{B}}$.

References in corpus (11)

• WSClean: an implementation of a fast, generic wide-field imager for radio astronomy
• An optimized algorithm for multi-scale wideband deconvolution of radio astronomical images
• LOFAR tied-array imaging of Type III solar radio bursts
• Estimation of a Coronal Mass Ejection Magnetic Field Strength using Radio Observations of Gyrosynchrotron Radiation
• Variable emission mechanism of a Type IV radio burst
• Moving solar radio bursts and their association with coronal mass ejections
• LOFAR observations of a jet-driven piston shock in the low solar corona
• An Eruptive Hot-Channel Structure Observed at Metric Wavelength as a Moving Type-IV Solar Radio Burst
• On the occurrence of type IV solar radio bursts in the solar cycle 24 and their association with coronal mass ejections
• Interferometric Imaging with LOFAR Remote Baselines of the Fine Structures of a Solar Type IIIb Radio Burst
• Exploring the circular polarisation of low-frequency solar radio bursts with LOFAR