Solar Radio Spikes and Type IIIb Striae Manifestations of Sub-second Electron Acceleration Triggered by a Coronal Mass Ejection

Abstract

Understanding electron acceleration associated with magnetic energy release at sub-second scales presents a major challenges in solar physics. Solar radio spikes observed as sub-second, narrow bandwidth bursts with $\Delta f/f\sim 10^{-3}-10^{-2}$ are indicative of sub-second evolution of the electron distribution. We present a statistical analysis of frequency, and time-resolved imaging of individual spikes and Type IIIb striae associated with a coronal mass ejection (CME). LOFAR imaging reveals that co-temporal ($<2$ s) spike and striae intensity contours almost completely overlap. On average, both burst types have similar source size with fast expansion at millisecond scales. The radio source centroid velocities are often superluminal, and independent of frequency over 30-45 MHz. The CME perturbs the field geometry, leading to increased spike emission likely due to frequent magnetic reconnection. As the field restores towards the prior configuration, the observed sky-plane emission locations drift to increased heights over tens of minutes. Combined with previous observations above 1 GHz, average decay time and source size estimates follow $\sim 1/f$ dependency over three decades in frequency, similar to radio-wave scattering predictions. Both time and spatial characteristics of the bursts between 30-70 MHz are consistent with radio-wave scattering with strong anisotropy of the density fluctuation spectrum. Consequently, the site of radio-wave emission does not correspond to the observed burst locations and implies acceleration and emission near the CME flank. The bandwidths suggest intrinsic emission source sizes $<1$ arcsec at 30 MHz, and magnetic field strengths a factor of two larger than average in events that produce decameter spikes.

Accepted for publication in the Astrophysical Journal (on 16 Feb 2023), 17 pages, 15 figures

References in corpus (12)

• Chromospheric magnetic field and density structure measurements using hard X-rays in a flaring coronal loop
• Dynamics of electron beams in the solar corona plasma with density fluctuations
• Millisecond microwave spikes: statistical study and application for plasma diagnostics
• Imaging Spectroscopy of Type U and J Solar Radio Bursts with LOFAR
• First Observation of a Type II Solar Radio Burst Transitioning Between a Stationary and Drifting State
• Simulations of radio-wave anisotropic scattering to interpret type III radio bursts measurements by Solar Orbiter, Parker Solar Probe, STEREO and Wind
• 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
• Interferometric Imaging with LOFAR Remote Baselines of the Fine Structures of a Solar Type IIIb Radio Burst
• Solar Fast Drifting Radio Bursts in an X1.3 Flare on 2014 April 25
• First Frequency-Time-Resolved Imaging Spectroscopy Observations of Solar Radio Spikes
• First imaging spectroscopy observations of solar drift pair bursts

Cited by in corpus (4)

• An Anisotropic Density Turbulence Model from the Sun to 1 au Derived From Radio Observations
• Source positions of an interplanetary type III radio burst and anisotropic radio-wave scattering
• Magnetic Field Geometry and Anisotropic Scattering Effects on Solar Radio Burst Observations
• Characterizing the Spectral Structure of Weak Impulsive Narrowband Quiet Sun Emissions