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G. M. Nita (New Jersey Institute of Technology), G. D. Fleishman (Ioffe Institute for Physics and Technology), D. E. Gary (New Jersey Institute of Technology)
A recent statistical study of 412 microwave burst spectra observed with OVSA during 2001-2002 (Nita, Gary and Lee 2004) revealed that about 16% of these spectra display a decimetric (dm) spectral component accompanying the centimetric (cm) emission. Rather surprisingly, most of the dm components display smooth spectra, with time scales comparable with those of their cm counterparts. In all considered events, the dm and cm spectral components are correlated in different aspects, so related to each other. We find no indication for these events of an anisotropic pitch-angle distribution, neither loss-cone nor beam-like, so no condition for any kinetic instability producing coherent radio emission is found. The dm component is likely produced by an incoherent emission mechanism, since its flux is proportional to the number of emitting electrons. The dm component is O-polarized, the degree of polarization being very large in some cases. We also find that the characteristic energy of fast electrons producing the dm continuum is significantly lower than the energy of the electrons generating the microwave gyrosynchrotron component. It appears that the spectral shape of the dm component is fairly independent of the fast electron distribution over energy. These findings agree well with the theoretical predictions for resonant transition radiation arising as a result of interaction of fast electrons and small-scale inhomogeneities of the background plasma, while they can hardly be interpreted within other known mechanisms of incoherent emission (like gyrosynchrotron, bremsstrahlung or inverse Compton). We discuss new possibilities of flaring plasma diagnostics with the use of these two-component bursts. This work is supported by NSF grant AST-0307670 to New Jersey Institute of Technology.
The author(s) of this abstract have provided an email address for comments about the abstract: gelu.m.nita@njit.edu
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Bulletin of the American Astronomical Society, 36 #2
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