Gamma-ray spectra from primary protons in a dipole magnetic field obtained in simulations with the GC approach. The primary protons released from the top of the reference magnetic field line are assumed to have an isotropic angular distribution and a power-law energy distribution with spectral indexes δ = 2 (left panel) and δ = 3 (right panel) in the range 1.0 MeV–1.0 GeV. The panels show the total spectrum, and the contributions from e⁺ annihilation, neutron-capture, proton inelastic processes, e^± bremsstrahlung, and π⁰ decay.