First Frequency-Time-Resolved Imaging Spectroscopy Observations of Solar Radio Spikes

Abstract

Solar radio spikes are short duration and narrow bandwidth fine structures in dynamic spectra observed from GHz to tens of MHz range. Their very short duration and narrow frequency bandwidth are indicative of sub-second small-scale energy release in the solar corona, yet their origin is not understood. Using the LOw Frequency ARray (LOFAR), we present spatially, frequency and time resolved observations of individual radio spikes associated with a coronal mass ejection (CME). Individual radio spike imaging demonstrates that the observed area is increasing in time and the centroid positions of the individual spikes move superluminally parallel to the solar limb. Comparison of spike characteristics with that of individual Type IIIb striae observed in the same event show similarities in duration, bandwidth, drift rate, polarization and observed area, as well the spike and striae motion in the image plane suggesting fundamental plasma emission with the spike emission region on the order of $\sim 10^8$ cm, with brightness temperature as high as $10^{13}$ K. The observed spatial, spectral, and temporal properties of the individual spike bursts are also suggesting the radiation responsible for spikes escapes through anisotropic density turbulence in closed loop structures with scattering preferentially along the guiding magnetic field oriented parallel to the limb in the scattering region. The dominance of scattering on the observed time profile suggests the energy release time is likely to be shorter than what is often assumed. The observations also imply that the density turbulence anisotropy along closed magnetic field lines is higher than along open field lines.

Accepted for publication in the Astrophysical Journal Letters (on 4 Aug 2021), 8 pages, 5 figures

References in corpus (8)

• Dynamics of electron beams in the solar corona plasma with density fluctuations
• First Observation of a Type II Solar Radio Burst Transitioning Between a Stationary and Drifting State
• Radio Echo in the Turbulent Corona and Simulations of Solar Drift-Pair Radio Bursts
• Sub-second time evolution of Type III solar radio burst sources at fundamental and harmonic frequencies
• Radio Spectral Imaging of an M8.4 Eruptive Solar Flare: Possible Evidence of a Termination Shock
• Detection of spike-like structures near the front of type-II bursts
• First imaging spectroscopy observations of solar drift pair bursts
• Narrowband Spikes Observed during the 2013 November 7 Flare

Cited by in corpus (4)

• An Anisotropic Density Turbulence Model from the Sun to 1 au Derived From Radio Observations
• Solar Radio Spikes and Type IIIb Striae Manifestations of Sub-second Electron Acceleration Triggered by a Coronal Mass Ejection
• The frequency ratio and time delay of solar radio emissions with fundamental and harmonic components
• Narrowband spikes observed during the 13 June 2012 flare in the 800-2000 MHz range