Diagnostics of interplanetary electron beams using X-ray and Radio data from Solar Orbiter

Energetic electrons accelerated by solar flares in the corona may propagate downward, produce X-rays in the chromosphere, and upward, producing coherent type III radio bursts in interplanetary space. Previous statistical studies of radio and X-ray flare observations have found a good temporal link between the two wavelengths but only a weak correlation between the intensities, in part due to the different emission mechanisms. Assuming both electron populations share properties from a common acceleration region, theory has predicted a link between the speed of the electron beams travelling outwards (deduced from radio) and the energy density of the electrons travelling downwards (deduced from X-rays). The Solar Orbiter mission is equipped with the STIX and RPW instruments, allowing for simultaneous observations of both X-ray and Radio emissions that can test this theory. We present results derived from the comparison of 35 flares observed by STIX in the 4-150 keV range associated in time with radio type III bursts detected by RPW (<10 MHz). From X-ray spectroscopy we obtained the electron spectrum of the associated HXR peak, from which the power can be estimated. We derived the Type III exciter speed using the rise and peak times of the time-profiles (V_r an V_p, respectively) in the 0.4-4 MHz range. We find the observed ratio V_r/V_p is 0.78 +- 0.06, complementing previous similar studies with observations at higher frequencies (30 – 70 MHz) and a ratio of 0.8+-0.06. We report a correlation between the power delivered by electrons with energies above 25 keV and V_r (cc=0.47), whilst a weaker one is obtained when comparing it with V_p (cc=0.2). There is an anticorrelation of the velocities V_p and V_r with the electron spectral index as expected, however the anticorrelation coefficients are weak. A weak correlation is also seen between the power (E>26keV) and the peak Radio intensities, the latter having strong correlations with electron spectral index (cc=0.71). Our results suggest that, whilst the electron acceleration maybe temporally correlated, the energy distribution of escaping and confined electrons for some events may depend on other parameters like the geometry of the reconnecting magnetic field.