LOFAR observations of fine spectral structure dynamics in type IIIb radio bursts

Abstract

Solar radio emission features a large number of fine structures demonstrating great variability in frequency and time. We present spatially resolved spectral radio observations of type IIIb bursts in the $30-80$ MHz range made by the Low Frequency Array (LOFAR). The bursts show well-defined fine frequency structuring called "stria" bursts. The spatial characteristics of the stria sources are determined by the propagation effects of radio waves; their movement and expansion speeds are in the range of 0.1-0.6c. Analysis of the dynamic spectra reveals that both the spectral bandwidth and the frequency drift rate of the striae increase with an increase of their central frequency; the striae bandwidths are in the range of ~20-100 kHz and the striae drift rates vary from zero to ~0.3 MHz s^-1. The observed spectral characteristics of the stria bursts are consistent with the model involving modulation of the type III burst emission mechanism by small-amplitude fluctuations of the plasma density along the electron beam path. We estimate that the relative amplitude of the density fluctuations is of dn/n~10^-3, their characteristic length scale is less than 1000 km, and the characteristic propagation speed is in the range of 400-800 km/s. These parameters indicate that the observed fine spectral structures could be produced by propagating magnetohydrodynamic waves.

References in corpus (13)

• LOFAR: The LOw-Frequency ARray
• Implications of X-ray Observations for Electron Acceleration and Propagation in Solar Flares
• Observing pulsars and fast transients with LOFAR
• Imaging Spectroscopy of Solar Radio Burst Fine Structures
• LOFAR tied-array imaging of Type III solar radio bursts
• Dynamics of electron beams in the solar corona plasma with density fluctuations
• LOFAR tied-array imaging and spectroscopy of solar S bursts
• Imaging Spectroscopy of Type U and J Solar Radio Bursts with LOFAR
• Statistical Survey of Type III Radio Bursts at Long Wavelengths Observed by the Solar TErrestrial RElations Observatory (STEREO)/Waves Instruments: Radio Flux Density Variations with Frequency
• The origin of the modulation of the radio emission from the solar corona by a fast magnetoacoustic wave
• Fine Structures of Solar Radio Type III Bursts and their Possible Relationship with Coronal Density Turbulence
• Coronal Alfven speeds in an isothermal atmosphere I. Global properties
• A tiny event producing an interplanetary type III burst

Cited by in corpus (25)

• Anisotropic Radio-Wave Scattering and the Interpretation of Solar Radio Emission Observations
• Magnetohydrodynamic Fast Sausage Waves in the Solar Corona
• CME-driven Shock and Type II Solar Radio Burst Band Splitting
• Statistics and Polarization of Type III Radio Bursts Observed in the Inner Heliosphere
• Coronal Quasi-periodic Fast-mode Propagating Wave Trains
• Evidence for Super-Alfvenic oscillations in sources of Solar type III radio bursts
• An Anisotropic Density Turbulence Model from the Sun to 1 au Derived From Radio Observations
• Fine structure of type III solar radio bursts from Langmuir wave motion in turbulent plasma
• A weak coronal heating event associated with periodic particle acceleration episodes
• 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
• Characterising coronal turbulence using snapshot imaging of radio bursts in 80-200 MHz
• Structured type III radio bursts observed in interplanetary space
• LOFAR observations of radio burst source sizes and scattering in the solar corona
• First Results from the REAL-time Transient Acquisition backend (REALTA) at the Irish LOFAR station
• First Frequency-Time-Resolved Imaging Spectroscopy Observations of Solar Radio Spikes
• Solar Radio Spikes and Type IIIb Striae Manifestations of Sub-second Electron Acceleration Triggered by a Coronal Mass Ejection
• First imaging spectroscopy observations of solar drift pair bursts
• Properties of Type III and Type IIIb Bursts in the Frequency Band of 8-80 MHz during PSP Perihelion at the Beginning of April 2019
• Preparing for Solar and Heliospheric Science with the SKAO: An Indian Perspective
• Interferometric imaging of the type IIIb and U radio bursts observed with LOFAR on 22 August 2017
• Magnetic Field Geometry and Anisotropic Scattering Effects on Solar Radio Burst Observations
• The frequency ratio and time delay of solar radio emissions with fundamental and harmonic components
• Sizes and shapes of sources in solar metric radio bursts