Physics
Scientific paper
Dec 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999spro.proc..211b&link_type=abstract
Solar Physics with Radio Observations, Proceedings of the Nobeyama Symposium, held in Kiyosato, Japan, Oct. 27-30, 1998, Edited
Physics
9
Scientific paper
Impulsive flares, by far the most common flares on the sun, impose strong demands on any theory of energy release and of particle acceleration. For a large flare, ~ 1037 electrons with energies >20 keV must be accelerated each second. These electrons produce hard X-rays by nonthermal bremsstrahlung emission and radio waves by plasma radiation processes and gyrosynchrotron emission. The hard X-ray emission is dominated by thick-target bremsstrahlung from fast electrons streaming directly from the acceleration site to the low corona and upper chromosphere, and by fast electrons precipitating from the magnetic trap. By contrast, microwave emission may be dominated by trapped electrons. In this paper, I briefly discuss the basic properties of microwave emission from impulsive flares: its morphology, source kinematics, and its relation to emissions at other wavelengths. I then summarize diagnostic uses of microwave emission and conclude with a description of recent work on the problem of the relative timing of HXR and microwave emission. It is shown that magnetic loops act as dispersive elements, allowing fixed-frequency observations to be used to probe electrons of differing energy. Spatially and temporally resolved observations of gyrosynchrotron emission from solar flares, such as those available from the Nobeyama Radioheliograph, enable one to constrain the evolution of the electron distribution function in time. I discuss some results of a comparative timing analysis of a sample of flares observed by the Nobeyama Radioheliograph and by the CGRO BATSE instrument.
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