Electron deceleration as a function of Thomson optical depth for different values of incoming beam Lorentz factor γ₀ for grey atmosphere. Blue, orange, green, and red curves correspond to energy losses due to Coulomb collisions and wave excitation for γ₀ = 2, 10, 50, and 500, respectively. The dashed lines show the same for energy losses where also bremsstrahlung is taken into account. The dotted line shows the result for γ₀ = 500 when we use a return-current-heated atmosphere instead of grey atmosphere (for model parameters given in Sect. 3.1). Inclusion of bremsstrahlung losses is found to be important for particles with γ₀ ≳ 100.