Ion Acceleration in Fermi-LAT Behind-the-Limb Solar Flares: The Role of Coronal Shock Waves

Abstract

We investigate the relationship between the gamma-ray emission measured with the Large Area Telescope on board Fermi (Fermi-LAT9 and radio signatures of coronal shock waves in four behind-the-limb (BTL) solar flares. All events were associated with metric type II radio bursts. Both start and end times of the radio bursts were synchronized with the gamma-ray emission. The type II bursts associated with the BTL gamma-ray flares had higher speeds and lower formation heights than those of an average sample. These findings support the notion that the highly relativistic ions that produce the gamma-rays in BTL flares are accelerated at CME-driven propagating coronal shock waves rather than in large-scale coronal loops.