Modeling the gamma-ray emission from the Sun

Despite its very close proximity to Earth and considerable previous study, there remain many unsolved puzzles about the Sun. One such example of significant recent interest relates to the GeV-TeV gamma-ray emission from the solar disk. Indeed, the only existing theoretical model can not fully explain the observed spectrum by Fermi Gamma-ray Space Telescope, which is significantly brighter and harder than predicted. Moreover, the theory fails to predict peculiar features of the observed gamma-ray flux, such as its anti-correlation with the solar cycle phases. Hence it is crucial to find a theoretical model that explains the mechanisms behind gamma-ray emission. The gamma-ray emission in this energy range is caused by the interaction of galactic cosmic rays with the solar atmosphere. Here we investigate the trajectories of sunward and anti-sunward moving GeV-TeV galactic cosmic rays (protons) as they move within the magnetic field near the solar surface. We performed numerical simulations through the PLUTO code for astrophysical fluid dynamics in which test-particle protons evolve on a static magnetic-arcade field model. Some protons are trapped as they gyrate around the magnetic arcades, some fall toward the Sun’s surface, and others escape the magnetic arcade region away from the Sun. We focus on the latter, as these particles escaping from the Sun can produce gamma rays that are observed at Earth.