New Evidence for Spatio-temporal Fragmentation in the Solar Flare Energy Release

Ramesh, R.; Mugundhan, V.; Prabhu, K.

doi:10.3847/2041-8213/ab6a9c

Cited by 7 publications

(4 citation statements)

References 46 publications

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“…Scattering of radio waves in the solar corona has been extensively studied since the first solar radio observations (Fokker 1965;Steinberg et al 1971;Steinberg 1972;Riddle 1974;Bougeret & Steinberg 1977;Robinson 1983;Bastian 1994;Arzner & Magun 1999;Thejappa et al 2007;Ramesh et al 2020). Consequently, Fokker (1965) performed the first numerical study of scattering on small-scale density inhomogeneities to estimate the apparent sizes and locations of solar radio-sources.…”

Section: Introductionmentioning

confidence: 99%

Subsecond Time Evolution of Type III Solar Radio Burst Sources at Fundamental and Harmonic Frequencies

Chen

Kontar

Chrysaphi

et al. 2020

ApJ

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Recent developments in astronomical radio telescopes opened new opportunities in imaging and spectroscopy of solar radio bursts at sub-second timescales. Imaging in narrow frequency bands has revealed temporal variations in the positions and source sizes that do not fit into the standard picture of type III solar radio bursts, and require a better understanding of radio-wave transport. In this paper, we utilise 3D Monte Carlo ray-tracing simulations that account for the anisotropic density turbulence in the inhomogeneous solar corona to quantitatively explain the image dynamics at the fundamental (near plasma frequency) and harmonic (double) plasma emissions observed at ∼32 MHz. Comparing the simulations with observations, we find that anisotropic scattering from an instantaneous emission point source can account for the observed time profiles, centroid locations, and source sizes of the fundamental component of type III radio bursts (generated where f pe ≈ 32 MHz). The best agreement with observations is achieved when the ratio of the perpendicular to the parallel component of the wave vector of anisotropic density turbulence is around 0.25. Harmonic emission sources observed at the same frequency (∼32 MHz, but generated where f pe ≈ 16 MHz) have apparent sizes comparable to those produced by the fundamental emission, but demonstrate a much slower temporal evolution. The simulations of radio-wave propagation make it possible to quantitatively explain the variations of apparent source sizes and positions at sub-second time-scales both for the fundamental and harmonic emissions, and can be used as a diagnostic tool for the plasma turbulence in the upper corona.

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Section: Introductionmentioning

confidence: 99%

Subsecond Time Evolution of Type III Solar Radio Burst Sources at Fundamental and Harmonic Frequencies

Chen

Kontar

Chrysaphi

et al. 2020

ApJ

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“…Electron beams injected onto a bundle of field lines propagate or are absorbed depending on the characteristics of the beams, the local plasma conditions, and the magnetic field geometry (Raoult et al, 1990;Reid and Kontar, 2015), so that an apparently simple type III burst observed with low spectral and temporal resolution is resolved into numerous bursts by more powerful instruments. Multiple sources in individual type III burst groups were found by Pick and Ji (1986) at meter wavelengths, spanning a typical angular width of 25 °(see also Pick and van den Oord, 1990;Paesold et al, 2001;Ramesh et al, 2020). The new VLA observations allowed for the first time to map the sources in detail and to determine subtelescopic sizes involved in the propagation.…”

Section: Evidence On Fragmented Energy Release and Particle Propagati...mentioning

confidence: 95%

Radio Astronomical Tools for the Study of Solar Energetic Particles I. Correlations and Diagnostics of Impulsive Acceleration and Particle Propagation

Klein

2021

Front. Astron. Space Sci.

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Solar energetic particles (SEPs) are sporadically ejected from the Sun during flares and coronal mass ejections. They are of major astrophysical interest, because the proximity of the Sun allows for detailed multi-messenger studies. They affect space weather due to interactions with electronics, with the Earth’s atmosphere, and with humans if they leave the protective shield of the magnetosphere of the Earth. Since early studies in the 1950s, starting with particle detectors on the ground, SEP events have been related to radio bursts. Two subjects are addressed in this chapter: attempts to establish quantitative correlations between SEPs and microwave bursts produced by gyro synchrotron radiation of mildly relativistic electrons, and the information derived from type III radio bursts on impulsive processes of particle acceleration and the coronal and interplanetary propagation. Type III radio bursts produced by electron beams on open magnetic field lines have a wide range of applications, including the identification of acceleration regions, the identification of confined particle acceleration with coronal signatures, but no SEPs, and the paths that the electrons, and energetic charged particles in general, take to travel from the low corona to the Heliosphere in case they escape. Simple scenarios of coronal particle acceleration are confirmed in relatively simple and short events. But the comparison with particle transport models shows that longer and delayed acceleration episodes exist especially in large SEP events. They will be discussed in a companion chapter.

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“…The brightness temperature (T b ) of the contours 1 & 2, estimated using the 'beam' size of the GRAPH at 80 MHz, are ≈3×10 5 K. The 'dots' inside the contours in Figure 3 correspond to the centroids of some of the individual type I bursts (see Figure 4). We located them following the methodology described in Ramesh et al (2020a). Any ionospheric refraction effects on the radio source positions in the present case are expected to be very minimal since the observations were carried out close to the local noon during which time the zenith angle of the Sun is the least.…”

Section: Observationsmentioning

confidence: 99%

Radio, X-ray and extreme-ultraviolet observations of weak energy releases in the `quiet' Sun

Ramesh,

Kathiravan,

Mithun

et al. 2021

Preprint

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We analyzed ground-based low frequency (<100 MHz) radio spectral and imaging data of the solar corona obtained with the facilities in the Gauribidanur observatory during the same time as the very weak soft X-ray flares (sub A-class, flux <10 −7 Wm −2 in the 1 -8 Å wavelength range) from the 'quiet' Sun observed with the X-ray Solar Monitor (XSM) onboard Chandrayaan-2 during the recent solar minimum. Non-thermal type I radio burst activity were noticed in close temporal association with the X-ray events. The estimated brightness temperature (T b ) of the bursts at a typical frequency like 80 MHz is ≈3×10 5 K. Extreme-ultraviolet (EUV) observations at 94 Å with the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) revealed a brightening close to the same location and time as the type I radio bursts. As far as we know reports of simultaneous observations of X-ray and/or EUV counterpart to weak transient radio emission at low frequencies from the 'quiet' Sun in particular are rare. Considering this and the fact that low frequency radio observations are sensitive to weak energy releases in the solar atmosphere, the results indicate that coordinated observations of similar events would be useful to understand transient activities in the 'quiet' Sun.

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New Evidence for Spatio-temporal Fragmentation in the Solar Flare Energy Release

Cited by 7 publications

References 46 publications

Subsecond Time Evolution of Type III Solar Radio Burst Sources at Fundamental and Harmonic Frequencies

Subsecond Time Evolution of Type III Solar Radio Burst Sources at Fundamental and Harmonic Frequencies

Radio Astronomical Tools for the Study of Solar Energetic Particles I. Correlations and Diagnostics of Impulsive Acceleration and Particle Propagation

Radio, X-ray and extreme-ultraviolet observations of weak energy releases in the `quiet' Sun

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