Deducing Electron Properties from Hard X-ray Observations
By E. P. Kontar, J. Brown, A. Emslie, W. Hajdas, Gordon D. Holman, G. Hurford, J. Kašparová, P. Mallik, A. Massone, M. McConnell and 4 more. 2011
167 citations recorded by the source corpus.
X-radiation from energetic electrons is the prime diagnostic of flare-accelerated electrons. The observed X-ray flux (and polarization state) is fundamentally a convolution of the cross-section for the hard X-ray emission process(es) in question with the electron distribution function, which is in turn a function of energy, direction, spatial location and time. To address the problems of particle propagation and acceleration one needs to infer as much information as possible on this electron distribution function, through a deconvolution of this fundamental relationship. This review presents recent progress toward this goal using spectroscopic, imaging and polarization measurements, primarily from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Previous conclusions regarding the energy, angular (pitch angle) and spatial distributions of energetic electrons in solar flares are critically reviewed. We discuss the role and the observational evidence of several radiation processes: free-free electron-ion, free-free electron-electron, free-bound electron-ion, photoelectric absorption and Compton backscatter (albedo), using both spectroscopic and imaging techniques. This unprecedented quality of data allows for the first time inference of the angular distributions of the X-ray-emitting electrons and improved model-independent inference of electron energy spectra and emission measures of thermal plasma. Moreover, imaging spectroscopy has revealed hitherto unknown details of solar flare morphology and detailed spectroscopy of coronal, footpoint and extended sources in flaring regions. Additional attempts to measure hard X-ray polarization were not sufficient to put constraints on the degree of anisotropy of electrons, but point to the importance of obtaining good quality polarization data in the future.
Subfields: Astronomy and Astrophysics, Pulmonary and Respiratory Medicine
View Paper: https://www.semanticscholar.org/paper/3602076f522ff772e7a00423c83a21d893fe4af0
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In Astronomy and Astrophysics
- L. Fletcher
- N. Vilmer
- Gordon D. Holman
- A. Emslie
- V. Petrosian
- E. P. Kontar
- G. Hurford
- Richard A. Schwartz
Citations in the corpus
- A review of solar type III radio bursts (2014, methodology): “We can use the X-ray signature to deduce the temporal, spatial, and energetic profile of the energised electrons (e.g. Kontar et al., 2011).”
- Recent Advances in Understanding Particle Acceleration Processes in Solar Flares (2011, methodology): “Further, as elaborated upon by Kontar et al. (2011), anisotropy in the mean electron distribution, combined with the intrinsic directivity of the bremsstrahlung emission process, produces an anisotropic distribution of primary photons.”
- The Spectrometer/Telescope for Imaging X-rays (STIX) (2020, background): “Hence, hard X-ray emissions provide ideal diagnostics of the hottest plasmas in solar flares and of the nonthermal tails seen at energies above the hottest thermal population (for reviews see Fletcher et al. 2011, Holman et al. 2011, Kontar et al. 2011).”
- Implications of X-ray Observations for Electron Acceleration and Propagation in Solar Flares (2011, background): “Issues related to the emission mechanism and deducing the properties of the emitting electrons from the X-ray observations are primarily addressed by Kontar et al. (2011).”