Radio and Hard X-Ray Images of High-Energy Electrons in an X-Class Solar Flare

Abstract

We present the first comparison between radio images of high-energy electrons accelerated by a solar flare and images of hard X-rays produced by the same electrons at photon energies above 100 keV. The images indicate that the high-energy X-rays originate at the footpoints of the loops dominating the radio emission. The radio and hard X-ray light curves match each other well and are quantitatively consistent with an origin in a single population of nonthermal electrons with a power-law index of around 4.5-5. The high-frequency radio spectral index suggests a flatter energy spectrum, but this is ruled out by the X-ray spectrum up to 8 MeV. The preflare radio images show a large hot long-lived loop not visible at other wavelengths. Flare radio brightness temperatures exceed 10(9) K, and the peak in the radio spectrum is as high as 35 GHz: both these two features and the hard X-ray data require very high densities of nonthermal electrons, possibly as high as 10(10) cm(-3) above 20 keV at the peak of the flare.