Origin and Location of the Hard X-Ray Emission in a Two-Ribbon Flare

Hoyng, P.; Duijveman, A.; Machado, M. E.; Rust, David M.; Švestka, Z.; Boelee, A.; Jager, C. de; Frost, K.; Lafleur, H.; Simnett, G. M.; Beek, H. F. van; Woodgate, B. E.

doi:10.1086/183574

Cited by 208 publications

(117 citation statements)

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“…In the context of interpreting flare loop hard X-ray footpoint sources (Hoyng et al 1981;Hudson & Fárník 2002), all contemporary flare models (Sturrock 1968;Kopp & Pneuman 1976;Shibata 1996;Turkmani et al 2005;Fletcher & Hudson 2008), regardless of their nature, assign a fundamental role during the flare energy release, transport and deposition to the high-energy non-thermal particle beams. In the impulsive phase of flares, the beams formed by charged particles are also guided from the acceleration site (wherever it is located) downwards along the magnetic field lines into the transition region, chromosphere and possibly photosphere.…”

Section: Introductionmentioning

confidence: 99%

Response of optical hydrogen lines to beam heating

Kašparová¹,

Varady²,

Heinzel³

et al. 2009

A&A

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Context. Observations of hydrogen Balmer lines in solar flares remain an important source of information on flare processes in the chromosphere during the impulsive phase of flares. The intensity profiles of optically thick hydrogen lines are determined by the temperature, density, and ionisation structure of the flaring atmosphere, by the plasma velocities and by the velocity distribution of particles in the line formation regions. Aims. We investigate the role of non-thermal electrons in the formation regions of Hα, Hβ, and Hγ lines in order to unfold their influence on the formation of these lines. We concentrate on pulse-beam heating varying on a subsecond timescale. Furthermore, we theoretically explore possibility that a new diagnostic tool exists indicating the presence of non-thermal electrons in the flaring chromosphere based on observations of optical hydrogen lines. Methods. To model the evolution of the flaring atmosphere and the time-dependent hydrogen excitation and ionisation, we used a 1-D radiative hydrodynamic code combined with a test-particle code that simulates the propagation, scattering, and thermalisation of a power-law electron beam in order to obtain the flare heating and the non-thermal collisional rates due to the interaction of the beam with the hydrogen atoms. To not bias the results by other effects, we calculate only short time evolutions of the flaring atmosphere and neglect the plasma velocities in the radiative transfer. Results. All calculated models have shown a time-correlated response of the modelled Balmer line intensities on a subsecond timescale, with a subsecond timelag behind the beam flux. Depending on the beam parameters, both line centres and wings can show pronounced intensity variations. The non-thermal collisional rates generally result in an increased emission from a secondary region formed in the chromosphere. Conclusions. Despite the clear influence of the non-thermal electron beams on the Balmer line intensity profiles, we were not able on the basis of our simulations to produce any unambiguous diagnostic of non-thermal electrons in the line-emitting region, which would be based on comparison of individual Balmer line intensity profiles. However, fast line intensity variations, well-correlated with the beam flux variations, represent an indirect indication of pulsating beams.

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Section: Introductionmentioning

confidence: 99%

Response of optical hydrogen lines to beam heating

Kašparová¹,

Varady²,

Heinzel³

et al. 2009

A&A

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“…In loop flares, this gives rise to H α ribbons in the photosphere that move apart with time. The combined information of the motion and the magnetic field distribution in the photosphere provides indirect information about the reconnection speed in the acceleration region (Hoyng et al 1981;Isobe et al 2002;Jing et al 2007;Liu et al 2008a;Liu & Wang 2009). In the reconnection model, one also expects the particles to be accelerated along the open field lines reaching into the upper corona.…”

Section: Introductionmentioning

confidence: 99%

Test particle acceleration in a numerical MHD experiment of an anemone jet

Rosdahl

Galsgaard²

2010

A&A

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Aims. To use a 3D numerical MHD experiment representing magnetic flux emerging into an open field region as a background field for tracing charged particles. The interaction between the two flux systems generates a localised current sheet where MHD reconnection takes place. We investigate how efficiently the reconnection region accelerates charged particles and what kind of energy distribution they acquire. Methods. The particle tracing is done numerically using the Guiding Center Approximation on individual data sets from the numerical MHD experiment. Results. We derive particle and implied photon distribution functions having power law forms, and look at the impact patterns of particles hitting the photosphere. We find that particles reach energies far in excess of those seen in observations of solar flares. However the structure of the impact region in the photosphere gives a good representation of the topological structure of the magnetic field.

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“…Therefore, observations in X-ray wavelengths give quantitative measures of heating and particle acceleration in the flare. X-ray observations by Hoyng et al (1981) showed hard X-ray (HXR) sources at both ends of a loop structure, commonly called footpoints. They are thick target bremsstrahlung emission produced by precipitating electrons, accelerated somewhere in the loop.…”

Section: Introductionmentioning

confidence: 99%

Relations between concurrent hard X-ray sources in solar flares

Battaglia¹,

Benz²

2006

A&A

114

134

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Context. Solar flares release a large fraction of their energy into non-thermal electrons, but it is not clear where and how. Bremsstrahlung X-rays are observed from the corona and chromosphere. Aims. We aim to characterize the acceleration process by the coronal source and its leakage toward the footpoints in the chromosphere. The relations between the sources reflect the geometry and constrict the configuration of the flare. Methods. We studied solar flares of GOES class larger than M1 with three or more hard X-ray sources observed simultaneously in the course of the flare. The events were observed with the X-ray satellite RHESSI from February 2002 until July 2005. We used imaging spectroscopy methods to determine the spectral evolution of each source in each event. The images of all of the five events show two sources visible only at high energies (footpoints) and one source only visible at low energies (coronal or looptop source, in two cases situated over the limb). Results. We find soft-hard-soft behavior in both, coronal source and footpoints. The coronal source is nearly always softer than the footpoints. The footpoint spectra differ significantly only in one event out of five. Conclusions. The observations are consistent with acceleration in the coronal source and an intricate connection between the corona and chromosphere.

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Origin and Location of the Hard X-Ray Emission in a Two-Ribbon Flare

Cited by 208 publications

References 0 publications

Response of optical hydrogen lines to beam heating

Response of optical hydrogen lines to beam heating

Test particle acceleration in a numerical MHD experiment of an anemone jet

Relations between concurrent hard X-ray sources in solar flares

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