Kontar, E.P., Dickson, E. and Kasparova, J. (2008) Low-energy cutoffs in electron spectra of solar flares: Statistical survey. Solar Physics, 252(1), pp. 139-147. (doi: 10.1007/s11207-008-9249-x)
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Abstract
The Reuven Ramaty High Energy Spectroscopic Imager (RHESSI) X-ray data base (February 2002 – May 2006) has been searched to find solar flares with weak thermal components and flat photon spectra. Using a regularized inversion technique, we determine the mean electron flux distribution from count spectra for a selection of events with flat pho- ton spectra in the 15 – 20 keV energy range. Such spectral behavior is expected for photon spectra either affected by photospheric albedo or produced by electron spectra with an ab- sence of electrons in a given energy range (e.g., a low-energy cutoff in the mean electron spectra of nonthemal particles). We have found 18 cases that exhibit a statistically signifi- cant local minimum (a dip) in the range of 13 – 19 keV. The positions and spectral indices of events with low-energy cutoff indicate that such features are likely to be the result of photo- spheric albedo. It is shown that if the isotropic albedo correction is applied, all low-energy cutoffs in the mean electron spectrum are removed, and hence the low-energy cutoffs in the mean electron spectrum of solar flares above ∼ 12 keV cannot be viewed as real features. If low-energy cutoffs exist in the mean electron spectra, their energies should be less than ∼ 12 keV.
| Item Type: | Articles |
|---|---|
| Status: | Published |
| Refereed: | Yes |
| Glasgow Author(s) Enlighten ID: | Kontar, Professor Eduard and Dickson, Mr Ewan and Kasparova, Dr Jana |
| Authors: | Kontar, E.P., Dickson, E., and Kasparova, J. |
| College/School: | College of Science and Engineering > School of Physics and Astronomy |
| Journal Name: | Solar Physics |
| ISSN: | 0038-0938 |
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