Probing Particle Acceleration through Gamma-ray Solar Flare Observations

TL;DR

This paper reviews how Fermi-LAT observations of solar flares, especially during the 24th cycle, enhance understanding of particle acceleration mechanisms and emission sites across different flare phases.

Contribution

It provides a comprehensive review of Fermi-LAT solar flare data and discusses how multi-wavelength observations help diagnose high-energy emission processes.

Findings

Detection of GeV emission from behind-the-limb flares

Extended >100 MeV emission lasting over 20 hours

Insights into spatially extended acceleration regions

Abstract

High-energy solar flares have shown to have at least two distinct phases: prompt-impulsive and delayed-gradual. Identifying the mechanism responsible for accelerating the electrons and ions and the site at which it occurs during these two phases is one of the outstanding questions in solar physics. Many advances have been made over the past decade thanks to new observational data and refined simulations that together help to shed light on this topic. For example, the detection by Fermi Large Area Telescope (LAT) of GeV emission from solar flares originating from behind the visible solar limb and >100 MeV emission lasting for more than 20 hours have suggested the need for a spatially extended source of acceleration during the delayed emission phase. In this work we will review some of the major results from Fermi-LAT observations of the 24th solar cycle and how this new observational channel combined with observations from across the electromagnetic spectrum can provide a unique opportunity to diagnose the mechanisms of high-energy emission and particle acceleration in solar flares.