Cumulative distribution of Γ₀ for GRBs with measured t_p (red solid line). The distribution of lower limits , derived for GRBs with an upper limit on the onset time , is shown by the dashed black curve (with rightward arrows). Assuming t_p ≥ T_p,γ the distribution of upper limits on Γ₀ is shown by the dotted grey line (with leftward arrows). The most stringent limit on the distribution of Γ₀ is shown by the green solid line which assumes that deceleration radius R_dec ≥ R(τ = 1), that is, the transparency radius (Eq. (16)). Joining estimates of Γ₀ and lower limits the reconstructed (through the KM estimator) distribution of Γ₀ is shown by the solid black line (and its 95% uncertainty by the yellow shaded region). The distributions are normalised to their respective number of elements. The two panels (right and left, respectively) show the case of a homogeneous (s = 0) and wind (s = 2) medium.