Energetic Solar Flare X-Rays Observed by Satellite and Their Correlation with Solar Radio and Energetic Particle Emission

Arnoldy, R. L.; Kane, S. R.; Winckler, J. R.

doi:10.1086/149470

Cited by 95 publications

(21 citation statements)

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“…The same beam of accelerated electrons should continuously emit via bremsstrahlung with the background plasma as it propagates from the corona. This thin-target emission (assuming no energy loss by the electrons) (Arnoldy et al 1968;Holt & Cline 1968;Takakura 1969;Lin & Hudson 1976) is again found to produce a power-law spectrum but this time with an index of γ CS = δ b + 1. So if the HXR emission of the electron beam was observable from the corona to the chromosphere then the acceleration and transport processes involved could be well constrained.…”

Section: Introductionmentioning

confidence: 73%

The spectral difference between solar flare HXR coronal and footpoint sources due to wave-particle interactions

Hannah

Kontar

2011

A&A

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Aims. We investigate the spatial and spectral evolution of hard X-ray (HXR) emission from flare accelerated electron beams subject to collisional transport and wave-particle interactions in the solar atmosphere. Methods. We numerically follow the propagation of a power-law of accelerated electrons in 1D space and time with the response of the background plasma in the form of Langmuir waves using the quasilinear approximation. Results. We find that the addition of wave-particle interactions to collisional transport for a transient initially injected electron beam flattens the spectrum of the footpoint source. The coronal source is unchanged and so the difference in the spectral indices between the coronal and footpoint sources is Δγ > 2, which is larger than expected from purely collisional transport. A steady-state beam shows little difference between the two cases, as has been previously found, as a transiently injected electron beam is required to produce significant wave growth, especially at higher velocities. With this transiently injected beam the wave-particle interactions dominate in the corona whereas the collisional losses dominate in the chromosphere. The shape of the spectrum is different with increasing electron beam density in the wave-particle interaction case whereas with purely collisional transport only the normalisation is changed. We also find that the starting height of the source electron beam above the photosphere affects the spectral index of the footpoint when Langmuir wave growth is included. This may account for the differing spectral indices found between double footpoints if asymmetrical injection has occurred in the flaring loop.

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Section: Introductionmentioning

confidence: 73%

The spectral difference between solar flare HXR coronal and footpoint sources due to wave-particle interactions

Hannah

Kontar

2011

A&A

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“…Traditionally, this energy transport has been attributed to beams of electrons travelling at semirelativistic speeds, a major strength of this hypothesis being that it is reasonably successful at explaining the basic features of chromospheric hard X-ray (HXR) emission (de Jager 1964;Arnoldy et al 1968;Brown 1971;Hudson 1972). Nonetheless, other energy transport mechanisms may also function during flares, with magnetohydrodynamic (MHD) waves being of particular interest (Emslie & Sturrock 1982;Fletcher & Hudson 2008).…”

Section: Introductionmentioning

confidence: 99%

Solar flares and focused energy transport by MHD waves

Russell

Stackhouse

2013

A&A

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Context. Transport of flare energy from the corona to the chromosphere has traditionally been assigned to electron beams; however, interest has recently been renewed in magnetohydrodynamic (MHD) waves as a complementary or alternative mechanism. Aims. We determine whether, and under what conditions, MHD waves deliver spatially localised energy to the chromosphere, as required if MHD waves are to contribute to emission from flare ribbons and kernels. This paper also highlights several properties of MHD waves that are relevant to solar flares and demonstrates their application to the flare problem. Methods. Transport is investigated using a magnetic arcade model and 2.5D MHD simulations. Different wave polarisations are considered and the effect of fine structuring transverse to the magnetic field is also examined. Ray tracing provides additional insight into the evolution of waveguided fast waves. Results. Alfvén waves are very effective at delivering energy fluxes to small areas of chromosphere, localisation being enhanced by magnetic field convergence and phase mixing. Fast waves, in the absence of fine coronal structure, are more suited to powering emission from diffuse rather than compact sources; however, fast waves can be strongly localised by coronal waveguides, in which case focused energy is best transported to the chromosphere when waveguides are directly excited by the energy release. Conclusions. MHD waves pass an important test for inclusion in future flare models.

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“…but with a spectral index γ tp = δ tp + 1, via thin-target emission (Arnoldy et al 1968;Holt & Cline 1968;Takakura 1969;Lin & Hudson 1976). If without energy loss, the same beam electrons will produce a power-law HXR spectrum with an index of γ ft = δ ft − 1 = δ tp − 1 via the thick-target emission (Brown 1971;Syrovatskii & Shmeleva 1972) when they travel to the chromosphere at the footpoint.…”

Section: Introductionmentioning

confidence: 99%

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

Chen

2013

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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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Energetic Solar Flare X-Rays Observed by Satellite and Their Correlation with Solar Radio and Energetic Particle Emission

Cited by 95 publications

References 0 publications

The spectral difference between solar flare HXR coronal and footpoint sources due to wave-particle interactions

The spectral difference between solar flare HXR coronal and footpoint sources due to wave-particle interactions

Solar flares and focused energy transport by MHD waves

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

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