Eleonora Puzzoni, University of Arizona
Title: “Role of magnetic arcades in explaining the gamma-ray emission from the Sun”
Abstract: In 1991, Seckel, Stanev, and Gaisser (SSG91) proposed a theoretical model aimed at predicting the gamma-ray emission originating from the solar disk from the interaction of Galactic Cosmic Rays (GCRs) with the solar atmosphere. However, the GeV-TeV gamma-ray emission remains an enigmatic and unresolved puzzle to date. Notably, observations by Fermi-LAT and HAWC present a gamma-ray emission with a brighter, harder spectrum extending to significantly higher energies than predicted by SSG91. The solution to this puzzle presumably lies in our understanding of how GCRs interact with solar magnetic fields in the corona and lower atmosphere and are thereby useful probes of this structure. Consequently, there is a pressing need for a new theoretical framework to comprehensively elucidate the mechanisms governing gamma-ray emission from the solar disk. This study focuses on exploring the impact of a closed magnetic field geometry on the observed gamma-ray flux. Numerical simulations, employing the PLUTO code, involve test-particle protons and depict the evolution of GCRs within a static magnetic arcade associated with an active region. Test-particle protons are injected at varying altitudes, accounting for the plausible migration of GCRs from adjacent flux tubes to closed arcade structures. A magnetic turbulent component is introduced into the arcade magnetic field, and multiple simulations explore increasing turbulence strengths. Our exploration focuses on understanding the influence of both the large-scale magnetic field within the arcade and its turbulent fluctuations on the trapping of particles. Our findings highlight a predominant gamma-ray emission pattern in the solar disk limb at higher energies and a more isotropic emission at lower energies, aligning with observations from Fermi-LAT. The resulting gamma-ray flux displays a discernible slope contingent upon the strength of turbulence. A comparative analysis with observations from Fermi-LAT and HAWC establishes a favorable agreement, bolstering the validity of our proposed model and affirming the consistency of our results with observations.