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Spectral evolution of microwaves and hard X-rays in the 1989 March 18 flare and its interpretationWe analyze the time variation of microwave spectra and hard X-ray spectra of 1989 March 18, which are obtained from the Solar Array at the Owens Valley Radio Observatory (OVRO) and the Hard X-Ray Burst Spectrometer (HXRBS) on the Solar Maximum Mission (SMM), respectively. From this observation, it is noted that the hard X-ray spectra gradually soften over 50 - 200 keV on-and-after the maximum phase while the microwaves at 1 - 15 GHz show neither a change in spectral shape nor as rapid a decay as hard X-rays. This leads to decoupling of hard X-rays from the microwaves in the decay phase away from their good correlation seen in the initial rise phase. To interpret this observation, we adopt a view that microwave-emitting particles and hard X-ray particles are physically separated in an inhomogeneous magnetic loop, but linked via interactions with the Whistler waves generated during flares. From this viewpoint, it is argued that the observed decoupling of microwaves from hard X-rays may be due to the different ability of each source region to maintain high energy electrons in response to the Whistler waves passing through the entire loop. To demonstrate this possibility, we solve a Fokker-Planck equation that describes evolution of electrons interacting with the Whistler waves, taking into account the variation of Fokker-Planck coefficients with physical quantities of the background medium. The numerical Fokker-Planck solutions are then used to calculate microwave spectra and hard X-ray spectra for agreement with observations. Our model results are as follows: in a sronger field region, the energy loss by electron escape due to scattering by the waves is greatly enhanced resulting in steep particle distributions that reproduce the observed hard X-ray spectra. In a region with weaker fields and lower density, this loss term is reduced allowing high energy electrons to survive longer so that microwaves can be emitted there in excess of hard X-rays during the decay phase of the flare. Our results based on spectral fitting of a flare event are discussed in comparison with previous studies of microwaves and hard X-rays based on either temporal or spatial information.
Document ID
19950038672
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Lee, Jeongwoo W.
(California Inst. of Tech., Pasadena, CA US, United States)
Gary, Dale E.
(California Inst. of Tech., Pasadena, CA US, United States)
Date Acquired
August 16, 2013
Publication Date
August 1, 1994
Publication Information
Publication: Solar Physics
Volume: 153
Issue: 2-Jan
ISSN: 0038-0938
Subject Category
Solar Physics
Accession Number
95A70271
Funding Number(s)
CONTRACT_GRANT: NAGW-3005
CONTRACT_GRANT: NSF ATM-90-13173
CONTRACT_GRANT: NAGW-1972
CONTRACT_GRANT: NSF AST-89-19770
Distribution Limits
Public
Copyright
Other

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