Correlation of Decimetric Radio Emission and Hard X-rays in Solar Flares

Details Correlation of Decimetric Radio Emission and Hard X-rays in Solar Flares Correlation of Decimetric Radio Emission and Hard X-rays in Solar Flares

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008espm...122.106d&link_type=abstract

"12th European Solar Physics Meeting, Freiburg, Germany, held September, 8-12, 2008. Online at http://espm.kis.uni-freiburg.de/,

Physics

Scientific paper

The emission of decimetric radiation, in particular narrowband spikes and pulsations, is generally considered to originate from particle acceleration processes in solar flares. On the other hand, non-thermal hard X-rays are well accepted results of such acceleration. Are radio emissions and hard X-rays 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 hard X-rays in solar flares was analyzed using data from the RHESSI spacecraft and the Phoenix-2 spectrometer of ETH Zürich. The Phoenix-2 spectrometer in Bleien (Switzerland) records the solar radio emission from 100 MHz to 4 GHz. We found 169 well observed joint decimetric events in the complete list of observations from February 2002 (date launch of the RHESSI satellite) to December 2006. About hundred radio events were of the type of pulsations, and in around thirty events we found were spikes. For the detailed analysis, 33 groups (26 radio events) of pulsations and 12 groups (11 radio events) of spikes were chosen.
The delay between the radio and hard X-rays emission was determined by cross-correlation. The time profiles of X-ray and radio emission differ much in energy and frequency. Thus correlation is not simply a yes/no question, but must be systematically searched in various ranges. The high spectral resolution of RHESSI made it possible to carefully choose the energy range, excluding thermal emission. The broad bandwidth of Phoenix-2 allowed selecting any emission in the full decimeter range. The energy range and duration in hard X-rays, and the frequency range in radio spectrograms were chosen to optimize the correlation. The cross-correlation coefficient was then analyzed by Gauss fit in delay for each event.
The mean delay for pulsations evaluated from Gauss fitting was found to be -1.50 seconds (minus indicates that hard X-rays emission comes first). The mean delay for narrowband spikes evaluated from Gauss fitting amounts to -2.25 seconds. The delays do not depend on position on the disk, duration of the correlating sequence and maximum value of cross-correlation coefficient. 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. This was not the case for pulsations.

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