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Deducing Electron Properties From Hard X-Ray Observations View all abstracts by submitter

Amir Caspi   Submitted: 2011-10-28 12:22

X-radiation from energetic electrons is the prime diagnostic offlare-accelerated electrons. The observed X-ray flux (and polarization state)is fundamentally a convolution of the cross-section for the hard X-ray emissionprocess(es) in question with the electron distribution function, which is inturn a function of energy, direction, spatial location and time. To address theproblems of particle propagation and acceleration one needs to infer as muchinformation as possible on this electron distribution function, through adeconvolution of this fundamental relationship. This review presents recentprogress toward this goal using spectroscopic, imaging and polarizationmeasurements, primarily from the Reuven Ramaty High Energy Solar SpectroscopicImager (RHESSI). Previous conclusions regarding the energy, angular (pitchangle) and spatial distributions of energetic electrons in solar flares arecritically reviewed. We discuss the role and the observational evidence ofseveral radiation processes: free-free electron-ion, free-freeelectron-electron, free-bound electron-ion bremsstrahlung, photoelectricabsorption and Compton back-scatter (albedo), using both spectroscopic andimaging techniques. This unprecedented quality of data allows for the firsttime inference of the angular distributions of the X-ray-emitting electronsusing albedo, improved model-independent inference of electron energy spectraand emission measures of thermal plasma. Moreover, imaging spectroscopy hasrevealed hitherto unknown details of solar flare morphology and detailedspectroscopy of coronal, footpoint and extended sources in flaring regions.Additional attempts to measure hard X-ray polarization were not sufficient toput constraints on the degree of anisotropy of electrons, but point to theimportance of obtaining good quality polarization data.

Authors: E.P. Kontar, J.C. Brown, A.G. Emslie, W. Hajdas, G.D. Holman, G. J. Hurford, J. Kasparova, P. C. V. Mallik, A. M. Massone, M. L. McConnell, M. Piana, M. Prato, E. J. Schmahl, E. Suarez-Garcia
Projects: GONG,Hinode/EIS,Hinode/SOT,Hinode/XRT,Nobeyama Radioheliograph,Owens Valley Solar Array,RHESSI,SDO-AIA,SDO-HMI,SDO-EVE,SoHO-EIT,SoHO-MDI,SoHO-CDS,SoHO-LASCO,SoHO-SUMER,STEREO,TRACE

Publication Status: Published -- Kontar, E. P., et al. 2011, Space Sci. Rev., 159, 301; DOI 10.1007/s11214-011-9804-x
Last Modified: 2011-11-17 14:20
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