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Gamma-ray emission and electron acceleration in solar flaresRecent observations have extended the spectra of the impulsive phase of flares to the GeV range. Such high-energy photons can be produced either by electron bremsstrahlung or by decay of pions produced by accelerated protons. In this paper we investigate the effects of processes which become important at high energies. We examine the effects of synchrotron losses during the transport of electrons as they travel from the acceleration region in the corona to the gamma-ray emission sites deep in the chromosphere and photosphere, and the effects of scattering and absorption of gamma rays on their way from the photosphere to space instruments. These results are compared with the spectra from so-called electron-dominated flares, observed by GRS on the Solar Maximum Mission, which show negligible or no detectable contribution from accelerated protons. The spectra of these flares show a distinct steepening at energies below 100 keV and a rapid falloff at energies above 50 MeV. Following our earlier results based on lower energy gamma-ray flare emission we have modeled these spectra. We show that neither the radiative transfer effects, which are expected to become important at higher energies, nor the transport effects (Coulomb collisions, synchrotron losses, or magnetic field convergence) can explain such sharp spectral deviations from a simple power law. These spectral deviations from a power law are therefore attributed to the acceleration process. In a stochastic acceleration model the low-energy steepening can be attributed to Coulomb collision and the rapid high-energy steepening can result from synchrotron losses during the acceleration process.
Document ID
19950039782
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Petrosian, Vahe
(Stanford University Stanford, CA, United States)
Mctiernan, James M.
(University of California, Berkeley, CA United States)
Marschhauser, Holger
(Max-Planck-Institut fuer Physik und Astrophysik Muenchen, Germany)
Date Acquired
August 16, 2013
Publication Date
October 20, 1994
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 434
Issue: 2
ISSN: 0004-637X
Subject Category
Solar Physics
Accession Number
95A71381
Funding Number(s)
CONTRACT_GRANT: NAGW-1976
CONTRACT_GRANT: NAGW-2452
CONTRACT_GRANT: NSF ATM-90-11628
Distribution Limits
Public
Copyright
Other

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