Particle trajectories and corresponding energies as functions of time for systems with two values of kρ₀ and four values of v_φ (b₀ = 15). Only the parts of trajectories before front crossing are shown. Trajectories are shown in eight separated small panels, while energies as functions of time are presented in two panels for two different kρ₀ values. For each trajectory the corresponding value of v_φ/v₀ is indicated inside the panels.