K.-L. Klein, A. Lekic, G. Trottet
LESIA, Observatoire de Paris-Meudon, 5 Place J. Janssen, F-92195
Meudon Cedex, France
Radio emission from non thermal electrons during solar microwave bursts is generally ascribed to gyrosynchrotron radiation from mildly relativistic electrons. The observed and modelled spectra usually show a maximum at frequencies of ten to a few tens of GHz, and a power-law shaped decay towards higher frequency. Several of the pioneering observations at sub-millimetre wavelengths from the Brazilian Solar Submillimter Telescope (Kaufmann et al) and the Swiss KOSMA instrument (Luethi et al) showed the surprising result of a spectral upturn near 300 GHz, to a maximum at sub-millimetre or far infrared wavelengths that are presently unobservable. There is a variety of possible interpretations of this rise. We explore here the idea, suggested by Kaufmann and Raulin (2006, Phys Plasmas) that the upturn is due to synchrotron radiation of highly relativistic electrons, and that the synchrotron spectrum might extend even into the X-ray range. We show results of simple numerical model calculations and discuss the impact of the synchrotron interpretation on the energies and numbers of relativistic electrons, as well as the flux densities expected at the yet unobserved far infrared wavelengths.