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

Abstract

Microwave and hard X-ray spectra provide crucial information about energetic electrons and their environment in solar flares. Both microwave and hard X-ray spectra are sensitive to cutoffs in the electron distribution function. The determination of the high-energy cutoff from these spectra establishes the highest electron energies produced by the acceleration mechanism, while determination of the low-energy cutoff is crucial to establishing the total energy in accelerated electrons. I present computations of the effects of both high- and low-energy cutoffs on microwave and hard X-ray spectra. The optically thick portion of a microwave spectrum is enhanced and smoothed by a low-energy cutoff, while a hard X-ray spectrum is flattened below the cutoff energy. A high-energy cutoff steepens the microwave spectrum and increases the wavelength at which the spectrum peaks, while the hard X-ray spectrum begins to steepen at photon energies an order of magnitude or more below the electron cutoff energy. I discuss how flare microwave and hard X-ray spectra can be analyzed together to determine these electron cutoff energies.