The effect of wave-particle interactions on low-energy cutoffs in solar flare electron spectra

Hannah, I.G., Kontar, E.P. and Sirenko, O.K. (2009) The effect of wave-particle interactions on low-energy cutoffs in solar flare electron spectra. Astrophysical Journal Letters, 707(1), pp. 45-50. (doi: 10.1088/0004-637X/707/1/L45)

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Solar flare hard X-ray (HXR) spectra from Reuven Ramaty High Energy Solar Spectrometer (RHESSI) are normally interpreted in terms of purely collisional electron beam propagation, ignoring spatial evolution and collective effects. In this Letter, we present self-consistent numerical simulations of the spatial and temporal evolution of an electron beam subject to collisional transport and beam-driven Langmuir wave turbulence. These wave-particle interactions represent the background plasma's response to the electron beam propagating from the corona to chromosphere and occur on a far faster timescale than Coulomb collisions. From these simulations, we derive the mean electron flux spectrum, comparable to such spectra recovered from high-resolution HXRs observations of solar flares with RHESSI. We find that a negative spectral index (i.e., a spectrum that increases with energy), or local minima when including the expected thermal spectral component at low energies, occurs in the standard thick-target model, when Coulomb collisions are only considered. The inclusion of wave-particle interactions does not produce a local minimum, maintaining a positive spectral index. These simulations are a step toward a more complete treatment of electron transport in solar flares and suggest that a flat spectrum (spectral index of 0-1) down to thermal energies maybe a better approximation instead of a sharp cutoff in the injected electron spectrum.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Kontar, Professor Eduard and Hannah, Dr Iain
Authors: Hannah, I.G., Kontar, E.P., and Sirenko, O.K.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal Letters
ISSN (Online):2041-8213
Published Online:23 November 2009
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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
398461Acceleration, propagation and emission of energetic particles from the sun to the earthEduard KontarParticle Physics & Astronomy Research Council (PPARC)PP/C001656/1Physics and Astronomy
465931Solar, stellar and cosmological plasmas: a synthesis of data, modelling and theory.Declan DiverScience & Technologies Facilities Council (STFC)ST/F002149/1Physics and Astronomy