Light curve for finite-duration emission. The case refers to an on-axis observer. The dashed colored light curves corresponding to n = 13 selected infinitesimal pulses out of the total N = 105 composing the finite-duration emission episode. Partial fluxes have been multiplied by a factor N/n in order to better visualize the contribution to the final emission at different radii. Colors identify the ΔR_0, i (Δt) with respect to the initial R₀ (t_em) at which the first pulse is emitted. The black solid line is the final light curve made by the sum of the partial ones. We assume a Gaussian jet with parameters Γ_c = 100, θ_c = θ_E = 3°, R₀ = 10¹³ cm and the pulse duration in the CoE frame ΔT = 10⁵ s. A SBPL spectrum with α_s = 0.2 and β_s = 1.3 is assumed.