Speaker
Description
First Name: Song
Last Name: Tan
Email Address: awarmuth@aip.de
Affiliation: Leibniz-Institute for Astrophysics Potsdam (AIP)
All Authors: Alexander Warmuth, Melissa Pesce-Rollins, NIcola Omodei, Song Tan
Abstract: Compared to energetic electrons in solar flares, which can be readily observed in hard X-rays and radio, our understanding of energetic ions is severely deficient. Our main diagnostics for ions are gamma-ray observations, which remain challenging. A particularly intriguing case are behind-the-limb (BTL) gamma-ray flares, where the flare is occulted as seen from Earth, but nevertheless gamma-ray emission is detected by near-Earth spacecraft. Here, we investigate the relationship between the gamma-ray emission measured with Fermi-LAT, hard X-ray observations from STIX on Solar Orbiter, and ground-based radio observations, for small sample of BTL gamma-ray flares. In all events, type II radio bursts were present that were synchronized in time with the gamma-ray emission. Conversely, we find a significant delay between the impulsive phase of the flare as recorded by STIX and the gamma-ray emission. 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.