Fermi Gamma-ray Space Telescope

Particle Transport in Behind-the-Limb Solar Flares

N. Omodei
M. Pesce-Rollins, on behalf of the Fermi-LAT collaboration

Abstract:

The recent detection of >100 MeV gamma rays from behind-the-limb solar flares has posed intriguing questions regarding the acceleration and transport of particles during these explosive phenomena. In order to produce gamma rays visible by the Fermi-LAT, high-energy particles need to travel to the visible side of the Sun and interact with the dense region close to the photosphere. In this contribution we show that particles accelerated several degrees behind the limb at an altitude of few solar radii, as in the case of a CME shock acceleration scenario, can be transported to the visible solar disk thanks to trapping and propagation along the solar magnetic field lines. Our simulations, based on particle-tracing, show that the main features observed in long duration solar flares, including the impulsive gamma-ray emission followed by the sustained gamma-ray emission and the Solar Energetic Particles detected at Earth, are well reproduced.