The Effects of Low‐ and High‐Energy Cutoffs on Solar Flare Microwave and Hard X‐Ray Spectra

Microwave and hard x-ray spectra provide crucial information about ener- getic electrons and their environment in solar flares. Both microwave and hard x-ray spectra are sensitive to cutos in the electron distribution function. The determination of the high-energy cuto from these spectra establishes the highest electron energies produced by the acceleration mechanism, while determination of the low-energy cuto is crucial to establishing the total energy in accelerated electrons. I present computations of the eects of both high- and low-energy cutos on microwave and hard x-ray spectra. The optically thick portion of a microwave spectrum is enhanced and smoothed by a low-energy cuto, while a hard x-ray spectrum is flattened below the cuto energy. A high-energy cuto steepens the microwave spectrum and increases the wavelength at which the spec- trum peaks, while the hard x-ray spectrum begins to steepen at photon energies an order of magnitude or more below the electron cuto energy. I discuss how flare microwave and hard x-ray spectra can be analyzed together to determine these electron cuto energies. Electrons are accelerated to high, suprathermal energies in solar flares. The total energy contained in these high-energy electrons may be as much as 10% or more of the total flare energy (Hudson & Ryan 1995). Most of these electrons are conned to magnetic loops in the low solar corona until they lose their energy through collisions with the dense plasma of the solar chromosphere and transition region. They are most directly observed through their gyrosynchrotron radiation at microwave frequencies and their bremsstrahlung at x- ray and -ray energies. The microwave emission is observed primarily from magnetic loops