Evolution of the apparent velocity as a function of the observation angle for a constant intensity profile (thick solid line) or an angular-dependent (Gaussian in the present case) intensity profile (thick dashed line). We use a Gaussian profile (D₃) for the Lorenz factor. For comparison, the case of a conical profile (D₁) and constant intensity is plotted in the thin line. The jet opening angle θ_j = 15° and γ₀ = 5.