Particle Acceleration in Solar Flares From Radio and Hard X-Ray Spectra

For a deeper understanding of the physical processes at play in solar flares, it is necessary to analyze the flare emissions at multiple wavelengths. This multifrequency approach enables the characterization of energetic electrons accelerated from hundreds of keV and up to several tens of MeV. This study reports on the observation of 10 solar flares, in which the spectral parameters were determined for the cm/mm and x-ray bands. The radio spectrum was fitted using gyrosynchrotron emission whereas the hard x-rays fit considered a model of thermal plus nonthermal emission of accelerated electrons. The results show that the spectral indices of the energy distribution of nonthermal electrons emitting in millimeter and hard x-rays do not agree, with the millimeter spectral index being approximately 2 units harder than that of hard x-rays. These findings are consistent with previous research and suggest the existence of a break in the energy spectrum of accelerated electrons. Moreover, for the only flare where photons exceeding 1 MeV were detected, the hard x-ray spectra exhibited a broken power-law where the index of the electron distribution above ~500 keV agreed with the inferred radio spectral index.