SOLAR MICROWAVE-BURSTS FROM ELECTRON POPULATIONS WITH A BROKEN ENERGY-SPECTRUM

Usually the gyrosynchrotron emission of microwave bursts from electron populations with a power-law (PL) energy distribution has been consid ered under the assumption that the spectral index of the distribution is constant over a wide range of energies. Meanwhile, there is strong evidence, in particular from hard X-ray and gamma-ray, but also from c m/mm wavelength radio observations, that in many solar flare events th e spectrum of the emitting electrons is characterized by a significant hardening at energies above 100-500 keV. We present some examples of calculated microwave burst spectra at cm/mm wavelengths taking into ac count the above evidence. It is shown that a break in the energy spect rum of the PL electrons can indeed result in a spectral hardening some times observed in microwave bursts at frequencies above 10-30 GHz.