Solar flare development during the impulsive phase as deduced from correlated radio and hard X-ray observations

Abstract

A correlative study of metric type III/V bursts and hard X-ray events during the preflash and the impulsive phases of solar flares is presented. A total of 55 groups of type III bursts were observed with the Nancay radiospectrograph, and 32 of these were associated with hard X-ray bursts detected with instruments on ISEE 3, SMM, or both. X-ray bursts associated with type III or U bursts, and type V continuum emission lasting less than 10 s are relatively small, with peak fluxes at 30 keV of not more than 1 photon/sq cm per sec per keV. X-ray bursts associated with type III bursts and continuum emission lasting longer than 30 s are considerably more intense, with peak fluxes at 30 keV exceeding 1 photon/sq cm per sec per keV and spectra extending to not less than 100 keV. For these latter events, type III emission was observed at 169 MHz with the Nancay radioheliograph from several locations during the preflash phase. At the time of the rapid increase in the hard X-ray flux, a new source appeared at 169 MHz and proceeded to fluctuate in phase with one of the original sources that brightened at the same time. This type of behavior, observed in 13 flares, is interpreted as being caused by the rapid interaction of two or more magnetic structures giving rise to the impulsive phase of the flare.