Atmosphere structure (left) and the spectrum of escaping radiation (right) for a power-law distribution of bombarding particles. Left panels: energy loss of the return current mQ⁺ and the temperature T dependence on the column density. The red curves correspond to δ = 1, the blue curves to δ = 2, and the black curves to δ = 3. Other parameters are given in Table 1. The dotted curves show the corresponding results when also the bremsstrahlung energy losses are taken into account. The dashed magenta curves correspond to the temperature structure and escaping spectrum of the atmosphere without external heating (almost completely overlapping the red solid curve).