Context. Flare-accelerated electrons may produce closely temporarily related hard X-ray emission while interacting with the dense
solar atmosphere and radio type III bursts when propagating from the low corona to the interplanetary medium. The link between
these emissions has been studied in previous studies. We present here new results on the correlation between the number and spectrum
of HXR producing electrons and the type III characteristics (flux, starting frequency).
Aims. The aim of this study is to extend the results from previous statistical studies of radio type III bursts and associated HXR
emissions: in particular what kind of correlation, if any, exists between the HXR emitting electron numbers and the radio flux? Are
there any correlations between the electron numbers or energy spectra deduced from associated HXR emissions and type III starting
Methods. This study is based on thirteen years of data between 2002 and 2014. We shortlisted ~ 200 events with close temporal
association between HXR emissions and radio type III bursts in the 450-150 MHz range. We used X-ray flare observations from
RHESSI and FERMI/GBM to calculate the number of electrons giving rise to the observed X-ray flux and observations from the
Nanšay Radioheliograph to calculate the peak radio flux at different frequencies in the 450-150 MHz range. Under the assumption
of thick-target emissions, the number of HXR producing electrons and their energy spectra were computed . The correlation between
electron numbers, power-law indices and the peak radio fluxes at different frequencies were analysed as well as potential correlations
between electron numbers and starting frequency of the radio burst. Bootstrap analysis for the correlation coeffcients was performed
to quantify the statistical significance of the fit.
Results. The correlation between the number of HXR electrons and the peak flux of the type III emission decreases with increasing
frequency. This correlation is larger when considering electron number above 20 keV rather than electron number above 10 keV. A
weak anticorrelation is also found between the absolute value of the electron spectral index and the peak radio flux at 228 MHz.
A rough correlation is found between the HXR producing electron number above 20 keV and the type III starting frequency. This
correlation is smaller if the electron number above 10 keV is considered. All the results are discussed in the framework of results from
previous studies and in the context of numerical simulations of bump-in-tail instabilities and subsequent radio emissions.
Authors: Tomin James & Nicole Vilmer
Publication Status: Astronomy and Astrophysics in press
Last Modified: 2023-03-29 14:54