Ion acceleration in Fermi-LAT behind-the-limb solar flares: the role of coronal shock waves

TL;DR

This study links gamma-ray emissions in behind-the-limb solar flares to coronal shock waves, showing that relativistic ions are likely accelerated by CME-driven shocks rather than coronal loops.

Contribution

It provides new evidence connecting gamma-ray emissions with high-speed, low-altitude coronal shock waves in behind-the-limb flares, highlighting the shock acceleration mechanism.

Findings

Gamma-ray emission times align with radio burst timings.

Type II radio bursts in BTL flares have higher speeds and lower formation heights.

Relativistic ions are accelerated by CME-driven shock waves.

Abstract

We investigate the relationship between the gamma-ray emission measured with Fermi-LAT and radio signatures of coronal shock waves in four behind-the-limb (BTL) solar flares. All events were associated with metric type II radio burst. 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.