Description
Energetic electrons from solar flares can move downward to produce X-rays in the chromosphere and upward to generate type III radio bursts in space. Previous studies found a good temporal correlation but a weak intensity correlation between both emissions due to different emission mechanisms. Theoretically, a link between the speed of outward electron beams (from radio) and the energy density of downward electrons (from X-rays) has been predicted. The Solar Orbiter mission, equipped with STIX and RPW instruments, allows for simultaneous X-ray and radio observations to test this theory.
We present results from 36 flares observed by STIX (4-150 keV) and associated with type III radio bursts detected by RPW (<10 MHz). Using X-ray spectroscopy, we obtained the electron spectral index and electron number during the HXR peak to estimate power. We derived the Type III exciter speed using the rise and peak times of the time profiles (V_front an V_peak, respectively) in the 0.4-4 MHz range, finding a V_p/V_f ratio of 0.77 ± 0.07, aligning with previous studies (@ 30-70 MHz, 0.8 ± 0.06) . We observed a correlation between electron power (E>25keV) and V_f (cc=0.48), and a weaker one with V_p (cc=0.3). The peak radio intensities correlate well with the electron spectral index (CC=0.72). These findings suggest that while electron acceleration is temporally correlated, the energy distribution of escaping and confined electrons may be influenced by the geometry of the reconnecting magnetic field. As predicted by simulations, the radio intensity increases with energy density in the accelerated beams.
