Timing properties of the line propagation in the outflow. A flash of monochromatic photons at 6.6 keV is simulated and propagated. Photons escaping from the bottom atmosphere without scattering are at 6.6 keV (see Fig. 1). The model parameters used here are ﹩kT_{e}=0.1﹩ keV, ﹩\beta =0.1﹩, and ﹩\tau =4﹩ (top) or 2 (bottom). We show the arrival time of photons at the top of the cloud for five energy bands, in free path time units ﹩t_{\mathrm{fp}\,}=l/ c﹩. Soft lags, low‐energy emission at later times, are clearly seen. The photon distribution over escape time integrated over energies can be fitted with an exponential law ﹩b\mathrm{exp}\,( -bt/ t_{\mathrm{fp}\,}) ﹩ (shown in Fig. 2). The values of ﹩b=0.057﹩ and 0.144 for ﹩\tau =4﹩ and 2, respectively (and consequently the average number of scatterings ﹩N_{\mathrm{av}\,}=1/ b﹩), are very close to b (or ﹩N_{\mathrm{av}\,}﹩) obtained from the best‐fit analytical spectrum for the same values of β and τ (see text).