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Benz, Christoph

doi:10.3139/9783446419216.004

Cited by 3 publications

(6 citation statements)

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“…We observed spikes spread across many frequencies, implying that the acceleration heights may vary, or that the electron beams have differing initial densities and spatial sizes that can increase the onset time and burst starting frequencies (Reid et al 2011;Reid & Kontar 2018b). The former agrees with the interpretation of spikes arising from many small sites of magnetic reconnection (Benz et al 1982;Benz 1985), which may have been triggered by the CME. The frequency at which a spike is observed could then be an interplay between the acceleration location, the initial beam properties, and the coronal turbulence that will promote Langmuir-wave growth at a specific region of space.…”

Section: Event Interpretationsupporting

confidence: 80%

“…Combined average spike bandwidth observations as a function of frequency are shown in Figure 12 (Markeev & Chernov 1971;Tarnstrom & Philip 1972b;Benz et al 1982;Benz 1985;Staehli & Magun 1986;Benz et al 1992;Csillaghy & Benz 1993;Benz et al 1996;Wang et al 1999;Messmer & Benz 2000;Wang et al 2002;Rozhansky et al 2008;Nita et al 2008;Wang et al 2008;Dábrowski et al 2011;Melnik et al 2014;Shevchuk et al 2016;Tan et al 2019) from 10 MHz to 8 GHz. Despite the possibility of over estimated average bandwidths at the higher frequencies due to limited spectral resolutions, the increase in Δf/f above 200 MHz is expected via consideration of the Langmuir-wave dispersion relation in a weakly magnetized plasma (Melrose 1985;Pécseli 2012;Melnik et al 2014;Shevchuk et al 2016)…”

Section: Bandwidthmentioning

confidence: 99%

“…Considering the narrow bandwidths with the plasma emission hypothesis implies that the production of Langmuir waves and stimulation of radio emission occurs over short distances that were previously suggested to be the result of weak electron beams-i.e., small spatial sizes and low beam densities (Tarnstrom & Philip 1972a;Melnik et al 2014). Previous studies have considered spike emission resulting from electron acceleration occurring in many small sites (Benz et al 1982) and the fragmentation of flare energy release (Benz 1985). At gigahertz frequencies, millisecond spikes are suggested to be produced via ECM emission in numerous sources due to magnetic inhomogeneities (Rozhansky et al 2008) that could produce fragmentation secondary to that of primary energy release (Fleishman & Mel'nikov 1998).…”

Section: Introductionmentioning

confidence: 99%

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Solar Radio Spikes and Type IIIb Striae Manifestations of Subsecond Electron Acceleration Triggered by a Coronal Mass Ejection

Clarkson

Kontar

Vilmer

et al. 2023

ApJ

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Understanding electron acceleration associated with magnetic energy release at subsecond scales presents major challenges in solar physics. Solar radio spikes observed as subsecond, narrow-bandwidth bursts with Δf/f ∼ 10−3–10−2 are indicative of a subsecond evolution of the electron distribution. We present a statistical analysis of frequency- and time-resolved imaging of individual spikes and Type IIIb striae associated with a coronal mass ejection (CME). LOFAR imaging reveals that the cotemporal (<2 s) spike and striae intensity contours almost completely overlap. On average, both burst types have a similar source size with a fast expansion at millisecond scales. The radio source centroid velocities are often superluminal and independent of frequency over 30–45 MHz. The CME perturbs the field geometry, leading to increased spike emission likely due to frequent magnetic reconnection. As the field restores itself toward the prior configuration, the observed sky-plane emission locations drift to increased heights over tens of minutes. Combined with previous observations above 1 GHz, the average decay time and source size estimates follow a ∼1/f dependence over three decades in frequency, similar to radio-wave scattering predictions. Both time and spatial characteristics of the bursts between 30 and 70 MHz are consistent with radio-wave scattering with a strong anisotropy of the density fluctuation spectrum. Consequently, the site of the radio-wave emission does not correspond to the observed burst locations and implies acceleration and emission near the CME flank. The bandwidths suggest intrinsic emission source sizes <1″ at 30 MHz and magnetic field strengths a factor of two larger than average in events that produce decameter spikes.

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Section: Event Interpretationsupporting

confidence: 80%

Section: Bandwidthmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Solar Radio Spikes and Type IIIb Striae Manifestations of Subsecond Electron Acceleration Triggered by a Coronal Mass Ejection

Clarkson

Kontar

Vilmer

et al. 2023

ApJ

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“…Their observational characteristics were described in many papers (e.g. Karlický 1984;Fu et al 1985;Stähli & Magun 1986;Benz et al 1982;Zlobec & Karlický 1998;Mészárosová et al 2003).…”

Section: Introductionmentioning

confidence: 99%

Successive Merging of Plasmoids and Fragmentation in a Flare Current Sheet and Their X-Ray and Radio Signatures

Karlický

Bárta

2011

ApJ

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Based on our recent MHD simulations, first, a concept of the successive merging of plasmoids and fragmentation in the current sheet in the standard flare model is presented. Then, using a 2.5-D electromagnetic particle-in-cell model with free boundary conditions, these processes were modelled on the kinetic level of plasma description. We recognized the plasmoids which mutually interacted and finally merged into one large plasmoid. Between interacting plasmoids further plasmoids and current sheets on smaller and smaller spatial scales were formed in agreement with the fragmentation found in MHD simulations. During interactions (merging -coalescences) of the plasmoids the electrons were very efficiently accelerated and heated. We found that after a series of such merging processes the electrons in some regions reached the energies relevant for the emission in the hard X-ray range. Considering these energetic electrons and assuming the plasma density 10 9 -10 10 cm −3 and the source volume as in the December 31, 2007 flare (Krucker at al. 2010), we computed the X-ray spectra as produced by the bremsstrahlung emission process. Comparing these spectra with observations, we think that these processes can explain the observed above-the-loop-top hard X-ray sources. Furthermore, we show that the process of a fragmentation between two merging plasmoids can generate the narrowband dm-spikes. Formulas for schematic fractal reconnection structures were derived. Finally, the results were discussed.

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“…Many people presented the investigations from observations and theoretical models. For the duration of single spikes, it is about 50 ∼ 100 ms around 250 MHz, 10 ∼ 50 ms around 460 MHz and 3 ∼ 7 ms around 1420 MHz (Benz et al 1982). Guedel & Benz (1990) present a detailed study of the temporal properties of single spikes and showed a negative correlation of the averaged duration of spike bursts with the frequency as τ ∝ f −1.34±0.14 at frequencies between ∼ 300-1000 MHz.…”

Section: Introductionmentioning

confidence: 99%

Evolvement of microwave spike bursts in a solar flare on 2006 December 13

Tang

Wan

et al. 2021

Res. Astron. Astrophys.

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Solar radio spikes are one of the most intriguing spectral types of radio bursts. Their very short lifetimes, small source size and super-high brightness temperature indicate that they should be involved in some strong energy release, particle acceleration and coherent emission processes closely related to solar flares. In particular, for the microwave spike bursts, their source regions are much close to the related flaring source region which may provide the fundamental information of the flaring process. In this work, we identify more than 600 millisecond microwave spikes which recorded by the Solar Broadband Radio Spectrometer in Huairou (SBRS/Huairou) during an X3.4 solar flare on 2006 December 13 and present a statistical analysis about their parametric evolution characteristic. We find that the spikes have nearly the same probability of positive and negative frequency drifting rates not only in the flare rising phase, but also in the peak and decay phases. So we suppose that the microwave spike bursts should be generated by shock-accelerated energetic electrons, just like the terminational shock (TS) wave produced by the reconnection outflows near the loop top. The spike bursts occurred around the peak phase have the highest central frequency and obviously weak emission intensity, which imply that their source region should have the lowest position with higher plasma density due to the weakened magnetic reconnection and the relaxation of TS during the peak phase. The right-handed polarization of the most spike bursts may be due to the TS lying on the top region of some very asymmetrical flare loops.

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Cited by 3 publications

References 0 publications

Solar Radio Spikes and Type IIIb Striae Manifestations of Subsecond Electron Acceleration Triggered by a Coronal Mass Ejection

Solar Radio Spikes and Type IIIb Striae Manifestations of Subsecond Electron Acceleration Triggered by a Coronal Mass Ejection

Successive Merging of Plasmoids and Fragmentation in a Flare Current Sheet and Their X-Ray and Radio Signatures

Evolvement of microwave spike bursts in a solar flare on 2006 December 13

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