Stroboscopic space–time diagram showing the evolution of the scaled surface density τ for an integration with the Pr76-parameters and an associated scaled torque . Brighter regions correspond to larger τ-values. The blue solid line marks the path of a signal traveling with the linear group velocity (Eq. (42)) starting from resonance r = r_L at time t = 0. Also shown are profiles of τ at different stages of the evolution. Due to the plot being stroboscopic, the density wave pattern eventually becomes stationary as the oscillation with frequency ω^s = −Ω_L is effectivelyremoved.