Radio Imaging of Signatures of Shock Accelerated Electrons during Coronal Mass Ejections

Diana Morosan, University of Helsinki

The Sun is an active star that produces the most powerful explosions in the solar system, solar flares, often accompanied by coronal mass ejections (CMEs) that drive collisionless shocks in the corona. CME shocks are efficient particle accelerators and shock signatures associated with CMEs are often observed as solar radio bursts, that move with the expanding CME. However, the relationship between radio shock signatures on the Sun and the expansion of a CME is still not well understood due to previous limitations of low radio frequency imaging (<200 MHz) where the most dramatic acceleration is believed to occur. Here, we exploit unique observations from the Low Frequency Array (LOFAR) of a strong X8.2-class solar flare and its associated very fast CME (3000 km/s). In particular, we image for the first time a multitude of radio shock signatures called herringbones with LOFAR. We also exploit another unique dataset from the Nancay Radioheliograph (NRH) of an M1.9-class flare associated with multiple moving radio bursts also accompanying a fast CME (1000 km/s). Using multi-wavelength analysis, we provide convincing evidence for shock accelerated electrons at multiple locations on the expanding CME flanks during the two separate coronal mass ejections observed.