Solar Disk Gamma-Ray Emission via Synthetic Magnetic Field from Photosphere to Low Corona

Gamma-ray emission in the GeV-TeV range from the solar disk is likely to arise from collisions of galactic cosmic rays (GCRs) with solar atmospheric plasma. In a previous study, we demonstrated that closed turbulent magnetic arcades trap GCRs efficiently, leading to a gamma-ray flux consistent with the Fermi-HAWC observations (from ∼0.1 GeV to ∼1 TeV). Here, we model a synthetic magnetic field with a static, laminar structure of open field lines in the chromosphere, increasingly braided near the solar surface, with a scale height of ∼10⁻² R_⊙. The height-dependent increase in magnetic field line braiding is modulated by an exponential scalar function, mimicking the bending of the photo- and chromospheric magnetic field revealed by polarimetric observations and reproduced by MHD simulations. Employing 3D test-particle numerical simulations, we investigate how distorted magnetic field lines affect the gamma-ray production by injecting GeV-TeV protons into both magnetically laminar and braided regions. We find that with the chosen spatial resolution, this synthetic magnetic field can account for the >10 GeV gamma-ray spectrum observed by Fermi/HAWC. A rebrightening between approximately 30 and 100 GeV (following a ∼30 GeV spectral dip) suggests an enhanced confinement within the photo-/chromospheric layer by stronger braiding.