Type III bursts produced by power law injected electrons in Maxwellian background coronal plasmas

Li, Bo; Cairns, Iver H.

doi:10.1002/jgra.50445

Cited by 23 publications

(22 citation statements)

References 75 publications

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“…The spread in the observed drift rates is too large to make any meaningful conclusions about whether multiple power-laws over different frequency ranges, used by , would be a better fit rather than a single power-law fit. The drift rates are also similar to simulated type III bursts at 85 MHz and > 100 MHz by Li et al (2008); Li & Cairns (2013).…”

Section: Drift Ratesupporting

confidence: 87%

“…The velocity of electron beams, as derived from type III bursts, has been reported to be slowing down as the beams propagate through the heliosphere (Fainberg et al 1972;Krupar et al 2015;Reiner & MacDowall 2015). The drift rate has been investigated using the onset time rather than the peak time observationally (Fainberg et al 1972;Dulk et al 1987;Reiner & MacDowall 2015) and numerically (Li & Cairns 2013) and a faster velocity was obtained, postulating that the front of the electron beam travels with a faster velocity. Derived electron beam velocities are also dependent upon the conditions of the background plasma, with Li & Cairns (2014) showing how a background Kappa distribution resulted in faster derived velocities than when the background had a Maxwellian distribution.…”

Section: Introductionmentioning

confidence: 99%

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Solar type III radio burst time characteristics at LOFAR frequencies and the implications for electron beam transport

Reid

Kontar

2018

A&A

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Context. Solar type III radio bursts contain a wealth of information about the dynamics of electron beams in the solar corona and the inner heliosphere; currently unobtainable through other means. However, the motion of different regions of an electron beam (front, middle and back) have never been systematically analysed before. Aims. We characterise the type III burst frequency-time evolution using the enhanced resolution of LOFAR in the frequency range 30-70 MHz and use this to probe electron beam dynamics. Methods. The rise, peak and decay times with a ∼ 0.2 MHz spectral resolution were defined for a collection of 31 type III bursts. The frequency evolution is used to ascertain the apparent velocities of the front, middle and back of the type III sources and the trends are interpreted using theoretical and numerical treatments. Results. The type III time profile was better approximated by an asymmetric Gaussian profile, not an exponential as previously used. Rise and decay times increased with decreasing frequency and showed a strong correlation. Durations were smaller than previously observed. Drift rates from the rise times were faster than from the decay times, corresponding to inferred mean electron beam speeds for the front, middle and back of 0.2, 0.17, 0, 15 c, respectively. Faster beam speeds correlate with smaller type III durations. We also find type III frequency bandwidth decreases as frequency decreases. Conclusions. The different speeds naturally explain the elongation of an electron beam in space as it propagates through the heliosphere. The rate of expansion is proportional to the mean speed of the exciter; faster beams expand faster. Beam speeds are attributed to varying ensembles of electron energies at the front, middle and back of the beam.

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Section: Drift Ratesupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Solar type III radio burst time characteristics at LOFAR frequencies and the implications for electron beam transport

Reid

Kontar

2018

A&A

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“…The simulations were restricted to frequencies above 150 MHz and the type III flux peaked above 200 MHz, which is inconsistent to the general trend of increasing flux with decreasing frequency reported in this and other studies. A further study by Li & Cairns (2013) demonstrated via an initial power-law electron beam that decreasing the power-law spectral index increased the fundamental radio flux emitted at high and low radio frequencies. Both sets of simulations can explain why a coronal burst produced by an electron beam with a smaller (harder) power-law spectral index, i.e.…”

Section: Interplanetary Bursts and >25 Kev Electronsmentioning

confidence: 99%

Coronal type III radio bursts and their X-ray flare and interplanetary type III counterparts

Reid

Vilmer

2017

A&A

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Context. Type III bursts and hard X-rays are both produced by flare energetic electron beams. The link between both emissions has been investigated in many previous studies, but no statistical studies have compared both coronal and interplanetary type III bursts with X-ray flares. Aims. Using events where the coronal radio emission above 100 MHz is exclusively from type III bursts, we revisited some longstanding questions regarding the relation between type III bursts and X-ray flares: Do all coronal type III bursts have X-ray counterparts? What correlation, if any, occurs between radio and X-ray intensities? What X-ray and radio signatures above 100 MHz occur in connection with interplanetary type III bursts below 14 MHz? Methods. We analysed ten years of data from 2002 to 2011 starting with a selection of coronal type III bursts above 100 MHz. We used X-ray flare information from RHESSI >6 keV to make a list of 321 events that have associated type III bursts and X-ray flares, encompassing at least 28% of the initial sample of type III events. We then examined the timings, intensities, associated GOES class, and whether there was an associated interplanetary radio signature in both radio and X-rays. Results. For our 321 events with radio and X-ray signatures, the X-ray emission at 6 keV usually lasted much longer than the groups of type III bursts at frequencies >100 MHz. The selected events were mostly associated with GOES B and C class flares. A weak correlation was found between the type III radio flux at frequencies below 327 MHz and the X-ray intensity at 25-50 keV, with an absence of events at high X-ray intensity and low type III radio flux. The weakness of the correlation is related to the coherent emission mechanism of radio type IIIs which can produce high radio fluxes by low density electron beams. Interplanetary type III bursts (<4 MHz) were observed for 54% of the events. The percentage of association increased when events were observed with 25-50 keV X-rays. A stronger interplanetary association was present when 25-50 keV RHESSI count rates were above 250 counts/s or radio fluxes of around 170 MHz were large (>10 3 SFU), relating to electron beams with more energetic electrons above 25 keV and events where magnetic flux tubes extend into the high corona. We also find that whilst on average type III bursts increase in flux with decreasing frequency, the rate of this increase varies from event to event.

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“…The first theory of plasma emission was put forth by Ginzburg & Zhelezniakov (1958) and many modifications and improvements have been made over the past six decades (Tsytovich 1967;Kaplan & Tsytovich 1968;Zheleznyakov & Zaitsev 1970;Melrose 1982;Goldman & Dubois 1982;Goldman 1983;Cairns 1987;Robinson & Cairns 1998;Mel'Nik et al 1999;Kontar 2001;Ledenev et al 2004;Li et al 2005Li et al , 2006aLi et al ,b, 2008aLi & Cairns 2013;. Although the essential theoretical framework based upon EM weak turbulence theory, which describes the entire process starting from the beam-generated Langmuir turbulence to the radiation generation, was available, complete numerical solution of the entire set of EM weak turbulence equations have not been done until quite recently, when Ziebell et al (2014aZiebell et al ( ,b,c, 2015 numerically solved the complete equations of EM weak turbulence theory for the first time.…”

Section: Introductionmentioning

confidence: 99%

Two-dimensional time evolution of beam-plasma instability in the presence of binary collisions

Tigik

Ziebell

Yoon

et al. 2016

A&A

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Energetic electrons produced during solar flares are known to be responsible for generating solar type III radio bursts. The radio emission is a byproduct of Langmuir wave generation via beam-plasma interaction and nonlinear wave-wave and wave-particle interaction processes. In addition to type III radio bursts, electrons traveling downwards toward the chromosphere lead to the hard X-ray emission via electron-ion collisions. Recently, the role of Langmuir waves on the X-ray-producing electrons has been identified as important, because Langmuir waves may alter the electron distribution, thereby affecting the X-ray profile. Both Coulomb collisions and wave-particle interactions lead electrons to scattering and energy exchange that necessitates considering the two-dimensional (2D) problem in velocity space. The present paper investigates the influence of binary collisions on the beam-plasma instability development in 2D in order to elucidate the nonlinear dynamics of Langmuir waves and binary collisions. The significance of the present findings in the context of solar physics is discussed.

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Type III bursts produced by power law injected electrons in Maxwellian background coronal plasmas

Cited by 23 publications

References 75 publications

Solar type III radio burst time characteristics at LOFAR frequencies and the implications for electron beam transport

Solar type III radio burst time characteristics at LOFAR frequencies and the implications for electron beam transport

Coronal type III radio bursts and their X-ray flare and interplanetary type III counterparts

Two-dimensional time evolution of beam-plasma instability in the presence of binary collisions

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