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

Abstract

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. 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.}{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.

10 pages, 10 FIgures, accepted for publication in A&A

References in corpus (13)

• RHESSI Microflare Statistics II. X-ray Imaging, Spectroscopy & Energy Distributions
• Relations between concurrent hard X-ray sources in solar flares
• Local re-acceleration and a modified thick target model of solar flare electrons
• Chromospheric magnetic field and density structure measurements using hard X-rays in a flaring coronal loop
• A Statistical Survey of Hard X-ray Spectral Characteristics of Solar Flares with Two Footpoints
• Dynamics of electron beams in the inhomogeneous solar corona plasma
• Solar wind density turbulence and solar flare electron transport from the Sun to the Earth
• The effect of wave-particle interactions on low energy cutoffs in solar flare electron spectra
• The sub-arcsecond hard X-ray structure of loop footpoints in a solar flare
• The x-ray detectability of electron beams escaping from the sun
• Exploring the connection between coronal and footpoint sources in a thin-thick target solar flare model
• Numerical consideration of quasilinear electron cloud dynamics in plasma
• Beam-plasma system and its X-ray directivity

Cited by in corpus (12)

• A Review of Solar Type III Radio Bursts
• Implications for electron acceleration and transport from non-thermal electron rates at looptop and footpoint sources in solar flares
• Wave-particle interactions in non-uniform plasma and the interpretation of Hard X-ray spectra in solar flares
• Evolution of the Solar Flare Energetic Electrons in the Inhomogeneous Inner Heliosphere
• Understanding breaks in solar flares x-ray spectra: Evaluation of a co-spatial return-current model
• Impulsive Phase Coronal Hard X-ray Sources in an X3.9 Class Solar Flare
• Effect of turbulent density-fluctuations on wave-particle interactions and solar flare X-ray spectra
• Role of Suprathermal Runaway Electrons Returning to the Acceleration Region in Solar Flares
• Comparative study of electric currents and energetic particle fluxes in a solar flare and Earth magnetospheric substorm
• Return currents and energy transport in the solar flaring atmosphere
• Electron Cyclotron Maser Emissions from Evolving Fast Electron Beams
• Twin Null-Point-Associated Major Eruptive Three-Ribbon Flares with Unusual Microwave Spectra