Energy release in a prominence-loaded flaring loop

Wheatland, M. S.; Melrose, D. B.

doi:10.1007/bf00733037

Cited by 27 publications

(35 citation statements)

References 4 publications

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“…In their stochastic acceleration model, the difference between the coronal and footpoint spectra is explained by the energy-dependent time scale for electrons to escape the acceleration region. The left panel of Figure 10.3 illustrates the model of Wheatland & Melrose (1995). The spatially integrated spectrum (violet) is the power-law spectrum (thick-target, γ thick = δ − 1) expected for a single-power-law electron distribution with no low-or high-energy cutoffs and no thermal component.…”

Section: Interpretation Of the Connection Between Footpoints And The mentioning

confidence: 98%

“…A simple 1-D model that described the coronal emission as intermediate thin-thick, depending on electron energy, was developed by Wheatland & Melrose (1995). In this model a high-density region ( 10 12 cm −3 ) is hypothesized to be present at or above the top of the flare loop.…”

Section: Interpretation Of the Connection Between Footpoints And The mentioning

confidence: 99%

“…They found that, after obtaining a power-law model spectrum with an index of γ = 3 that agreed with the observed footpoint spectra, the effective spectral index of the coronal source from the model (γ = 4.7) was significantly steeper than that obtained for the flare (γ = 4). Battaglia & Benz (2007) compared the model of Wheatland & Melrose (1995) to the results of their study of five flares observed by RHESSI. The right panel of Figure 10.3 shows observed spectra and spectral fits for one particular event.…”

Section: Interpretation Of the Connection Between Footpoints And The mentioning

confidence: 99%

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Implications of X-ray Observations for Electron Acceleration and Propagation in Solar Flares

et al. 2011

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High-energy X-rays and γ-rays from solar flares were discovered just over fifty years ago. Since that time, the standard for the interpretation of spatially integrated flare X-ray spectra at energies above several tens of keV has been the collisional thick-target model. After the launch of the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) in early 2002, X-ray spectra and images have been of sufficient quality to allow a greater focus on the energetic electrons responsible for the X-ray emission, including their origin and their interactions with the flare plasma and magnetic field. The result has been new insights into the flaring process, as well as more quantitative models for both electron acceleration and propagation, and for the flare environment with which the electrons interact. In this article we review our current understanding of electron acceleration, energy loss, and propagation in flares. Implications of these new results for the collisional thick-target model, for general flare models, and for future flare studies are discussed.

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Section: Interpretation Of the Connection Between Footpoints And The mentioning

confidence: 98%

Section: Interpretation Of the Connection Between Footpoints And The mentioning

confidence: 99%

Section: Interpretation Of the Connection Between Footpoints And The mentioning

confidence: 99%

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Implications of X-ray Observations for Electron Acceleration and Propagation in Solar Flares

et al. 2011

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“…Most studies have, however, been theoretical proposals or numerical simulations, based on standard flare values, that do not attempt to explain or reproduce true solar flare observations. Battaglia & Benz (2007) compared RHESSI spectra to the ITTT-model of Wheatland & Melrose (1995), demonstrating that the qualitative shape and relations between coronal and footpoint-spectrum often do not agree with the model predictions. In this study, we take an additional step by completing a quantitative analysis of the relation linking coronal and footpoint spectra in the context of the thin-thick target model; we demonstrate that, in some cases, electric fields related to return currents can indeed explain the relation between coronal and footpoint spectra.…”

Section: Introductionmentioning

confidence: 99%

Observational evidence for return currents in solar flare loops

Battaglia

Benz

2008

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Context. The common flare scenario comprises an acceleration site in the corona and particle transport to the chromosphere. Using satellites available to date it has become possible to distinguish between the two processes of acceleration and transport, and study the particle propagation in flare loops in detail, as well as complete comparisons with theoretical predictions. Aims. We complete a quantitative comparison between flare hard X-ray spectra observed by RHESSI and theoretical predictions. This enables acceleration to be distinguished from transport and the nature of transport effects to be explored. Methods. Data acquired by the RHESSI satellite were analyzed using full sun spectroscopy as well as imaging spectroscopy methods. Coronal source and footpoint spectra of well observed limb events were analyzed and quantitatively compared to theoretical predictions. New concepts are introduced to existing models to resolve discrepancies between observations and predictions. Results. The standard thin-thick target solar flare model cannot explain the observations of all events. In the events presented here, propagation effects in the form of non-collisional energy loss are of importance to explain the observations. We demonstrate that those energy losses can be interpreted in terms of an electric field in the flare loop. One event seems consistent with particle propagation or acceleration in lower than average density in the coronal source. Conclusions. We find observational evidence for an electric field in flare loops caused by return currents.

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“…In particular, they find that in two of those events, A&A 550, A63 (2013) the differences at specific times, as well as the time-averaged difference, were significantly more than two, ruling out a simple thin-thick target interpretation. A possible explanation for the discrepancy is that there was an anomalously high density concentrated at the looptop source in the corona so that this emission is a combination of thin-thick target, which would result in a flatter footpoint spectral index at low energies, namely Δγ > 2 (Battaglia & Benz 2007), as previously suggested by Wheatland & Melrose (1995) for the coronal HXR sources observed by Yohkoh/HXT (Masuda et al 1994;Feldman et al 1994). However this model predicts a break in the coronal HXR spectrum between the thin and thick target range, which has not been observed with RHESSI data despite its high energy resolution.…”

Section: Introductionmentioning

confidence: 88%

Anomalous resistivity in beam-return currents and hard-X ray spectra of solar flares

Chen

2013

A&A

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Context. Observations of hard-X ray (HXR) spectra from solar flares show that there is noncollisional energy loss when energetic beam electrons are transported along the flare loop from their acceleration site above the looptop in the corona to the loop footpoints in the chromosphere. Aims. This paper investigates anomalous (i.e., noncollisional) resistivity due to the effective collision by the wave-particle interaction in the beam-return current system of a flare and its effect on the HXR spectral evolution between the looptop and footpoint sources. Methods. To attribute the noncollisional energy loss to an induced electric field by the beam current, the induced electric field is estimated by the spectral evolution between the looptop and footpoint sources, which is deduced from the standard thin-thick target model. To include collisional and anomalous resistivity caused by the ion-acoustic wave turbulence excited by the return current, the necessary excited level and the excited condition are discussed for the steady-state case in which the return current density driven by the induced electric field in terms of Ohm's law is required to be equal to the beam current density. Results. The results show that including the anomalous resistivity can reasonably remove the discrepancy between observations and predictions. Meanwhile, the necessary excited level for the ion-acoustic turbulence is tens times of the thermal noise of electrostatic fluctuations in the background plasma, which is an ordinary and low excited level that is easily satisfied. Conclusions. This indicates that the microscopic kinetics of plasma particles possibly play an important and critical role in understanding the dynamics of beam-return current systems in the solar atmosphere and in the physics of solar flares.

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Energy release in a prominence-loaded flaring loop

Cited by 27 publications

References 4 publications

Implications of X-ray Observations for Electron Acceleration and Propagation in Solar Flares

Implications of X-ray Observations for Electron Acceleration and Propagation in Solar Flares

Observational evidence for return currents in solar flare loops

Anomalous resistivity in beam-return currents and hard-X ray spectra of solar flares

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