Small electron acceleration episodes in the solar corona

James, Tomin; Subramanian, Prasad; Kontar, Eduard P.

doi:10.1093/mnras/stx1460

Cited by 18 publications

(16 citation statements)

References 44 publications

(58 reference statements)

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“…As the energy contained in the deca-keV elec-trons increases, the corresponding radio brightness temperature increases. The energies obtained are quite small, in comparison to those measured at 1 AU (Krucker et al 2007;James et al 2017). However the durations of our electrons beams are significantly lower than those estimated at 1AU, with the number of electrons per second of our largest simulations being comparable to James et al (2017) at 74 keV.…”

Section: Frequency Log Amplitude Spectralcontrasting

confidence: 61%

Spatial Expansion and Speeds of Type III Electron Beam Sources in the Solar Corona

Reid

Kontar

2018

ApJ

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A component of space weather, electron beams are routinely accelerated in the solar atmosphere and propagate through interplanetary space. Electron beams interact with Langmuir waves resulting in type III radio bursts. Electron beams expand along the trajectory, and using kinetic simulations, we explore the expansion as the electrons propagate away from the Sun. Specifically, we investigate the front, peak and back of the electron beam in space from derived radio brightness temperatures of fundamental type III emission. The front of the electron beams travelled at speeds from 0.2c-0.7c, significantly faster than the back of the beam that travelled between 0.12c-0.35c. The difference in speed between the front and the back elongates the electron beams in time. The rate of beam elongation has a 0.98 correlation coefficient with the peak velocity; in-line with predictions from type III observations. The inferred speeds of electron beams initially increase close to the acceleration region and then decrease through the solar corona. Larger starting densities and harder initial spectral indices result in longer and faster type III sources. Faster electron beams have higher beam energy densities, produce type IIIs with higher peak brightness temperatures and shorter FWHM durations. Higher background plasma temperatures also increase speeds, particularly at the back of the beam. We show how our predictions of electron beam evolution influences type III bandwidth and drift-rates. Our radial predictions of electron beam speed and expansion can be tested by the upcoming in situ electron beam measurements made by Solar Orbiter and Parker Solar Probe.

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Section: Frequency Log Amplitude Spectralcontrasting

confidence: 61%

Spatial Expansion and Speeds of Type III Electron Beam Sources in the Solar Corona

Reid

Kontar

2018

ApJ

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“…in the case of less pitch-angle scattering, an effect that can reduce the determined number of escaping electrons, the anisotropic sample does indeed contain on average higher numbers of escaping in situ electrons. In contrast to results by James et al (2017), who used data by ACE/EPAM (Gold et al 1998) and determined a fraction of 6 to 148% of escaping electrons compared to the HXRproducing electrons our results confirm the findings by Krucker et al (2007). We find very small fractions of escaping electrons with mean ratios of only 0.18% for all events and 0.24% for the anisotropic events.…”

Section: Total Number Of Escaping Electronssupporting

confidence: 67%

Connecting solar flare hard X-ray spectra to in-situ electron spectra using RHESSI and STEREO/SEPT observations

Dresing¹,

Warmuth²,

Effenberger³

et al. 2021

Preprint

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In-situ observations of solar energetic particle events are determined by a combination of acceleration, injection, and transport processes which are often hard to disentangle. However, the energy spectrum of impulsive electron events is believed to carry the imprint of the flare acceleration process which can be studied by analyzing the hard X-ray (HXR) spectrum of the flare.Using STEREO/SEPT electron data of the whole STEREO mission we have identified 64 solar energetic electron event candidates where the HXR solar counterpart of the event was observed by RHESSI. After cleaning of the data set and an independent verification by the timing of associated interplanetary type III radio bursts, we find 17 events which lend themselves for a comparison of the spectral indices observed in situ and at the Sun.Special attention is paid to the choice of the in-situ electron spectral index used for comparison as most of the events show spectral transitions (breaks) in the measurement range of SEPT. We find that both the lower and higher spectral indices correlate similarly well with the HXR spectra yielding correlation coefficients of 0.8 but indicating opposite relations with the flare spectrum in terms of the thin- or thick target model. The correlations show no dependence on the electron onset delay, nor on the longitudinal separation between flare and spacecraft magnetic footpoint at the Sun. However, the correlations increase, if only events with significant anisotropy are used indicating that transport effects play a role in shaping the spectra observed in-situ. We will discuss the different transport effects that need to be taken into account and which may even lead to a vanishing imprint of the flare acceleration.

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“…Similarly, the energy density in the nonthermal electron population per burst is only ≈ 10 −7 -10 −3 times that in the thermal population. This may be contrasted with the"cold" small acceleration events studied by James et al (2017), where the lack of soft Xray emission associated with their events implies that the acceleration process produced mostly nonthermal electrons (and very few thermal ones). We find that the power expended in accelerating the electrons responsible for a representative noise storm burst ranges from 10 21 to 10 24 erg s −1 and the energy contained in the accelerated electrons that produced a representative burst ranges from 10 20 to 10 23 erg (table 4).…”

Section: Discussionmentioning

confidence: 81%

Energetics of small electron acceleration episodes in the solar corona from radio noise storm observations

James

Subramanian

2018

Monthly Notices of the Royal Astronomical Society

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Observations of radio noise storms can act as sensitive probes of nonthermal electrons produced in small acceleration events in the solar corona. We use data from noise storm episodes observed jointly by the Giant Metrewave Radio Telescope (GMRT) and the Nancay Radioheliograph (NRH) to study characteristics of the nonthermal electrons involved in the emission. We find that the electrons carry 10 21 to 10 24 erg/s, and that the energy contained in the electrons producing a representative noise storm burst ranges from 10 20 to 10 23 ergs. These results are a direct probe of the energetics involved in ubiquitous, small-scale electron acceleration episodes in the corona, and could be relevant to a nanoflare-like scenario for coronal heating.

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Small electron acceleration episodes in the solar corona

Cited by 18 publications

References 44 publications

Spatial Expansion and Speeds of Type III Electron Beam Sources in the Solar Corona

Spatial Expansion and Speeds of Type III Electron Beam Sources in the Solar Corona

Connecting solar flare hard X-ray spectra to in-situ electron spectra using RHESSI and STEREO/SEPT observations

Energetics of small electron acceleration episodes in the solar corona from radio noise storm observations

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