Issn 1845–8319 on the Relation between Decimetric and Hard X-ray Emissions in the Impulsive Flare Phase

The emission of decimetric flare radiation, in particular narrowband spikes and pulsations, is generally considered to originate from accelerated, non-thermal particles. On the other hand, non-thermal hard X-rays (HXR) are well accepted results of such acceleration. Are radio emissions and HXR signatures of the same acceleration process? Good correlation of the light curves in the radio and HXR range may evidence it. The correlation of decimetric radio emission and HXR in solar flares was analyzed using data from the RHESSI spacecraft and the Phoenix-2 spectrometer in Bleien (Switzerland). For the first time we have the possibility of a systematic search on the radio-HXR relation in the range from 100 MHz to 4 GHz. The measured delays have a distribution with a FWHM of 4.9 s and 4.7 s for pulsations and spikes, respectively, evaluated from a Gauss fitting method. The mean delay for pulsations was found to be −1.4±0.9 seconds (minus indicates that hard X-rays emission comes first), and for narrowband spikes to −2.5± 2.5 seconds. The delays do not depend on centre frequency, cross-correlation coefficient, duration of the correlating sequence and position on the disk. However, we find an increase in delay for the spikes with GOES magnitude (peak soft X-ray emission) of the flare and with peak hard X-ray flux.