Estimation of solar disk gamma-ray emission based on Geant4

The most important astrophysical mechanism for steady solar gamma-ray emission is the interaction of cosmic rays with solar atmosphere, which has been definitely detected by Fermi-LAT with maximum energy up to 200 GeV. Some studies shown that the effect of the solar magnetic field to solar disk gamma-ray flux is unneglectable. It is valuable to study the physical mechanism between solar disk gamma-ray flux and solar magnetic field. In this paper, we simulated the interaction between cosmic rays and solar atmosphere by G4SOLAR program based on Geant4. A simulated solar disk gamma-ray flux from 1GeV to 1TeV was obtained with taking into account the influence of coronal magnetic field. The PFSS model for “quiet”Sun was employed, and the solar disk gamma-ray below 10GeV was consistent with the Fermi observation. But the simulated spectrum became much softer than Fermi data when >10GeV. Some influence factors were briefly discussed.