Nonthermal electrons in the thick-target reverse-current model for hard X-ray bremsstrahlung

Solar Physics ◽  
1991 ◽  
Vol 131 (2) ◽  
pp. 319-336 ◽  
Author(s):  
Yu. E. Litvinenko ◽  
B. V. Somov
Keyword(s):  
Current Model ◽  
Reverse Current ◽  
Thick Target ◽  
X Ray ◽  
Nonthermal Electrons

Electron Acceleration in Collapsing Magnetic Traps during the Solar Flare on July 19, 2012: Observations and Models

2017 ◽  
Vol 13 (S335) ◽  
pp. 90-93
Author(s):  
P. A. Gritsyk ◽  
B. V. Somov
Keyword(s):  
Point Source ◽  
Solar Flares ◽  
High Efficiency ◽  
Reverse Current ◽  
Electron Acceleration ◽  
Thick Target ◽  
Two Dimensions ◽  
Magnetic Traps ◽  
Thin Target ◽  
X Ray

AbstractUsing the appropriate kinetic equation, we considered the problem of propagation of accelerated electrons into the solar corona and chromosphere. Its analytical solution was used for modelling the M7.7 class limb flare occurred on July 19, 2012. Coronal above-the-loop-top hard X-Ray source was interpreted in the thin-target approximation, the foot-point source - in the thick-target approximation with account of the reverse-current electric field. For the foot-point source we found a good accordance with the RHESSI observations. For the coronal source we also got very accurate estimate of the power-law spectral index, but significant differences between the modelled and observed hard X-ray intensities were noticed. The last discrepancy was solved by adding the coronal magnetic trap model to the thin target model. The former one implies that the trap collapses in two dimensions, locks and accelerates particles inside itself. In our report, we confirm an existence and high efficiency of the electron acceleration in collapsing magnetic traps during solar flares. Our new results represent (e.g. for RHESSI observations) the theoretical prediction of the double step particle acceleration in solar flares, when the first step is the acceleration in reconnection area and the second one – the acceleration in coronal trap.

scholarly journals Current Status of the Dissipative Thermal Model for Solar Hard X-Ray Bursts

1985 ◽  
Vol 107 ◽  
pp. 509-512
Author(s):  
Dean F. Smith
Keyword(s):  
Thermal Model ◽  
Impulsive Phase ◽  
Thick Target ◽  
Current Status ◽  
Thermal Source ◽  
X Rays ◽  
Coulomb Collisions ◽  
Ambient Plasma ◽  
X Ray ◽  
Nonthermal Electrons

Up until about five years ago all models for hard X-ray bursts consisted of streaming nonthermal electrons interacting with an ambient plasma (Brown 1975). Even in its most efficient form of thick-target emission in which electrons are stopped in the ambient plasma, this type of model is very inefficient because the electrons lose about 105 times more energy in Coulomb collisions with the ambient plasma than in X-rays resulting from bremsstrahlung. As a result, according to the latest estimates, at least 20% of the dissipated flare energy must go into accelerated electrons at the peak of the impulsive phase (Duijveman et al. 1982). Stimulated by observations of hard X-rays with thermal spectra (Crannel et al. 1978; Elcan 1978), analysis of a thermal model in which all the electrons in a given volume are heated to a temperature Te = 108K was begun (Brown et al. 1979; Smith and Lilliequist 1979; Vlahos and Papadopoulos 1979). It was recognized from the beginning that some electrons in the tail of the distribution would escape through the conduction fronts formed and mimic nonthermal streaming electrons. This thermal model with loss of electrons or dissipation became known as the dissipative thermal model (Emslie and Vlahos 1980). If the escaping electrons are not replenished, they will cease to make a contribution after a fraction of a second and the source will become a pure thermal source. It will be shown below that collisional replenishment (Smith and Brown 1980) is too slow.

A comparison of the thick-target model with stereo data on the height structure of solar hard x-ray bursts

Solar Physics ◽  
1983 ◽  
Vol 88 (1-2) ◽  
Author(s):  
J.C. Brown ◽  
V.A. Carlaw ◽  
D. Cromwell ◽  
S.R. Kane
Keyword(s):  
Thick Target ◽  
X Ray ◽  
Target Model ◽  
Stereo Data

scholarly journals X-ray Emission from Hot DA White Dwarfs; EXOSAT Results, and Implications for Atmospheric Models

1989 ◽  
Vol 114 ◽  
pp. 198-201
Author(s):  
Frits Paerels ◽  
John Heise
Keyword(s):  
Systematic Uncertainty ◽  
Effective Temperature ◽  
White Dwarfs ◽  
Current Model ◽  
Broad Band ◽  
Model Calculations ◽  
X Ray ◽  
Transmission Grating ◽  
Upper Limit ◽  
Optical Flux

AbstractWe present the observations of the photospheric X-ray spectra of hot DA white dwarfs, obtained with the 500 lines mm−1 Transmission Grating Spectrometer on EXOSAT. These spectra cover the full soft X-ray band, at high wavelength resolution and statistical quality. They allow us to do an accurate measurement of the photospheric parameters, particularly of effective temperature and chemical composition of the atmosphere.We consider the case of HZ 43 in some detail. Model atmospheric spectra that satisfy all measured absolute optical, UV and X-ray fluxes turn out not to fit the shape of the measured X-ray spectrum. However, from a comparison of model spectra calculated with different model atmospheres codes we infer the existence of a 15% systematic uncertainty in the model fluxes at the shortest wavelengths (λ < 100 Å) in current model calculations. This can explain the fitting problem. Since the systematic uncertainty in the models is larger than the statistical uncertainty in the shape of the measured X-ray spectrum of HZ 43, we cannot at present use this measured shape to derive the effective temperature and gravity. We revert to broad band photometry, using the measured integrated soft X-ray flux and the optical flux, to determine Te = 45,000 – 54,000K, R/R⊙ = 0.0140 – 0.0165. From the absence of the He II Ly edge at 227 Å in the measured spectrum, we set a upper limit on the photospheric helium abundance of He/H = 1.0 × 10−5; this upper limit is independent of the uncertainties in the model calculations mentioned above.

scholarly journals III. Solar Maximum Mission Results

1985 ◽  
Vol 19 (1) ◽  
pp. 64-68
Author(s):  
M. E. Machado
Keyword(s):  
Impulsive Phase ◽  
Thick Target ◽  
Spectral Lines ◽  
The Novel ◽  
Line Broadening ◽  
Ongoing Research ◽  
X Ray ◽  
Chromospheric Evaporation ◽  
High Resolution Images ◽  
Beam Mechanism

The ongoing research carried out by the solar community has been reported in the proceedings of several recent symposia, seminars and workshops, as well as in scientific journals (Kane et al. 1983, Švestka et al. 1982a, Shea et al. 1984, Kundu S Woodgate 1984, Simon 1984). We summarize here some of the novel results with reference to flare research as far as SMM data analysis is concerned. Understanding of impulsive phase phenomena was one of the primary goals of the SMM. The early reports from the analysis of the first ever obtained high-resolution images in the <30 keV energy range stressed the fact that some flares showed hard x-ray (HXR) bright sources at the feet of coronal loops (Hoyng et al. 1981a, b, Machado et al. 1982, Duijveman et al. 1982), the so-called HXR “footpoints,” favoring the thick-target beam mechanism for the production of HXRs, and indicating acceleration efficiencies >20% during the early impulsive phase. This phenomenon was shown to be accompanied by soft x-ray (SXR) line broadening, indicative of strong turbulence, and the immediate appearance of blue shifted spectral lines, which shows that plasma heated to >10-1 K rises from the footpoints of loops with velocities to 300 km s-1 (Antonucci et al. 1982, Antonucci et al. 1984a). This result provides a strong indication of the chromospheric evaporation phenomenon, which has been confirmed in analyses of combined SXR and Ha observations (Acton et al. 1982, Gunkler et al. 1984).

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