A New Look at Type-III Bursts and Their Use as Coronal Diagnostics

Beltran, Samuel Tun; Cutchin, S.; White, S. M.

doi:10.1007/s11207-015-0760-6

Cited by 15 publications

(13 citation statements)

References 18 publications

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“…These more sensitive instruments provide fine-grained data over wide bandwidths and are already enabling new and interesting studies (e.g. Oberoi et al 2011;Morosan et al 2014;Tun Beltran et al 2015, and many others). The data from these new instruments provides fertile new ground to explore for presence of weak non-thermal emissions and their suitability for coronal heating.…”

Section: Introductionmentioning

confidence: 99%

Quantifying Weak Nonthermal Solar Radio Emission at Low Radio Frequencies

Sharma

Oberoi

Arjunwadkar

2018

ApJ

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The recent availability of fine grained high sensitivity data from the new generation low radio frequency instruments such as the Murchison Widefield Array (MWA) have opened up opportunities for using novel techniques for characterizing the nature of solar emission at these frequencies.Here we use this opportunity to look for evidence for the presence of weak non-thermal emissions in the 100-240 MHz band, at levels weaker than have usually been probed. The presence of such features is believed to be a necessary consequence of nanoflare-based coronal and chromospheric heating theories. We separate the calibrated MWA solar dynamic spectra into a slowly varying and an impulsive, and hence non-thermal, component. We demonstrate that Gaussian mixtures modeling can be used to robustly model the latter and we estimate the flux density distribution as well as the prevalence of impulsive non-thermal emission in the frequency-time plane. Evidence for presence of non-thermal emission at levels down to ∼0.2 SFU (1 SFU = 10 4 Jy) is reported, making them the weakest reported emissions of this nature. Our work shows the fractional occupancy of the non-thermal impulsive emission to lie in the 17-45% range during a period of medium solar activity. We also find that the flux density radiated in the impulsive non-thermal emission is very similar in strength to that of the slowly varying component, dominated by the thermal bremsstrahlung. Such significant prevalence and strength of the weak impulsive non-thermal emission has not been appreciated earlier.

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Section: Introductionmentioning

confidence: 99%

Quantifying Weak Nonthermal Solar Radio Emission at Low Radio Frequencies

Sharma

Oberoi

Arjunwadkar

2018

ApJ

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“…These arrays are already producing new and interesting science results enabled by their novel capabilities (e.g. Morosan et al Tun Beltran, Cutchin, and White, 2015;Suresh et al, 2017). Not only do they provide powerful tools to study longstanding problems like the generation and evolution of various known types of radio bursts, but they also open up new phase space with significant discovery potential.…”

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confidence: 99%

4D Data Cubes from Radio-Interferometric Spectroscopic Snapshot Imaging

Mohan

Oberoi

2017

Sol Phys

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The new generation of low radio-frequency interferometric arrays have enabled the imaging of the solar corona at high spectro-temporal resolutions and sensitivity. In this article we introduce and implement a formalism to generate flux density and brightness temperature ($T_{\mathrm B}$) maps from such images, using independently obtained disc-integrated solar flux density dynamic spectra. These images collectively generate a 4D data cube, with axes spanning angular coordinates ($\theta,\phi$), frequency ($\nu$) and time ($t$). This 4D data cube is the most informative data product which can be generated from interferometric radio data. It will allow us to track solar emission simultaneously in these four dimensions. We also introduce SPatially REsolved Dynamic Spectra (SPREDS), named in analogy to the usual dynamic spectra. For any arbitrary region, ($\theta_i,\phi_j$), in the maps, these 2D projections of the 4D data cube correspond to the dynamic spectrum of emission arising from there. We show examples of these data products using observations from the Murchison Widefield Array (MWA). These are also the first calibrated solar maps from the MWA

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“…The frequency spectrum for the overdense plasma, on the other hand, is single peaked at the plasma frequency ω e and shows no significant variation with the propagation angle θ. These spectral properties with respect to the parameters G and θ are probably relevant to type III burst observations (Beltran et al, 2015).…”

Section: 1029/2018ja025887mentioning

confidence: 76%

“…Another point of interest is the observation of spectral fine structures in type III bursts as striae (Beltran et al, ; Reid & Ratcliffe, , and references therein) which are possibly related to the described mechanism of electromagnetic wave generation. Mode splitting at the coupling points (see Figure c) together with the more or less periodic energy transfer between the participating waves offers the possibility of generating fine structures.…”

Section: Relevance To Observationsmentioning

confidence: 99%

Parametric Decay of Beam‐Generated Langmuir Waves and Three‐Wave Interaction in Plateau Plasmas: Implications for Type III Radiation

et al. 2019

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Inspired by the results of particle‐in‐cell simulations on beam‐plasma interaction, we present a mechanism for the generation of radio waves in solar type III bursts which provides a closed chain of the conversion processes from beam‐generated Langmuir waves into electromagnetic emission. The mechanism is characterized by two key steps. The first is a hitherto unknown parametric decay process in which the primary wave directly decays to low‐k Langmuir waves (plasma oscillations) and ion acoustic waves. This decay becomes possible due to changes in the dispersion properties of longitudinal waves initiated by the presence of a beam or a plateau in the electron velocity distribution. A resonant three‐wave interaction is established between the beam‐induced Langmuir wave, the plasma oscillations, and the ion acoustic wave. Due to weak damping of the waves involved, this interaction persists after the beam has relaxed to a plateau and lasts as long as the latter exists. In the second step, low‐k Langmuir waves in the range of “optical wavelengths” can linearly couple to obliquely propagating radio waves at the plasma frequency in a wave number region around the cross points where quasi‐longitudinal and quasi‐transverse modes approach each other. Our model does not need the persistence of the beam and the associated instability for radiation to be produced. Although the theory is local with respect to the plasma frequency, it may open a way to overcome Sturrock's () dilemma of rapid beam relaxation on the one side and long‐lived radiation on the other. The observed frequency variation is suggested to arise by “adiabatic” motion of the beam‐created interaction region through the heliospheric plasma of decreasing electron density. Implications for the interpretation of in situ Langmuir waveforms and the diversity of their frequency spectra are discussed.

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A New Look at Type-III Bursts and Their Use as Coronal Diagnostics

Cited by 15 publications

References 18 publications

Quantifying Weak Nonthermal Solar Radio Emission at Low Radio Frequencies

Quantifying Weak Nonthermal Solar Radio Emission at Low Radio Frequencies

4D Data Cubes from Radio-Interferometric Spectroscopic Snapshot Imaging

Parametric Decay of Beam‐Generated Langmuir Waves and Three‐Wave Interaction in Plateau Plasmas: Implications for Type III Radiation

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