Solar radio blips and X-ray kernels

Abstract

Hudson¹ proposed that the primary flare energy release goes into fast electrons. Others^2,3 found the flare soft X-ray emission to consist of bright, small kernels (knots and loops) embedded in a more diffuse halo. These kernels with a typical size of 5′ arc s and a temperature of 6–12 × 10⁶K emit in radio waves at 3.7 and 11 cm (ref. 4). The discovery of a radio brightness temperature equal to the temperature derived from the X rays and the radio size larger than in X rays shows that the observed radio emission is thermal (free–free) and the source optically thick at λ > 3.7 cm. Therefore, Kundu et al.⁴ did not observe the fast electrons expected to heat the kernels. Here we present high time resolution measurements at 2.8 cm from the Effelsberg 100-m telescope and at decimetric and metric wavelengths with the ETH Zurich spectrometers. Both instruments have detected signatures of non-thermal particles.