Atmosphere structure (left) and the spectrum of the escaping radiation (right) for mono-energetic return current. Left panels: dependence of the electron number density n_e, energy loss of the return current mQ⁺, and the temperature T on the column density. The red curves correspond to a model with Lorentz factor γ₀ = 500, the blue curves are for γ₀ = 50, and the black curves are for γ₀ = 10. The parameters are T_eff, h = 5 MK, T_eff, i = 1.6 MK, and log g = 14.3. The corresponding structure and the spectrum for model without external heating (T_eff, i = 5 MK, T_eff, h = 0) are shown with the magenta dashed curve.