Effect of the diffusion coefficient on the Geminga’s halo properties. Left: Spectral energy distribution of the Geminga pulsar halo for the synchrotron and ICS emissions, as integrated within an angular radius of 0.2° and 10°, respectively, for different values of the diffusion coefficient at 1 GeV (D₀). Right: Surface brightness of the Geminga synchrotron halo integrated over the energy range E_γ = [10–40] keV for different D₀. The inset shows the flux profile normalised at θ = 0, in arbitrary units.