Equal arrival time rings (top panels) and corresponding light curves (bottom panels) for three configurations of the viewing angle (from left to right), θ_v = 0° (on-axis), θ_v = θ_c (edge-of-the-core), and θ_v = 3 × θ_c (off-axis). Top panels: polar plot of the emitting surface. The black circle shows the physical limit of the core of the jet. The black cross shows the observer line of sight. The colored curves are the EATRs at ten arbitrary sampling times. Bottom panels: light curve normalized at its maximum value (corresponding to the on-axis observer at the first sampled epoch). The colored dots represent the flux emitted by the corresponding colored EATRs in the top panel. The structured jet assumed for this test case has a Gaussian structure with Γ_c = 100, θ_c = θ_E = 3°, R₀ = 10¹⁵ cm. The comoving emission spectrum is described by a SBPL spectrum with α_s = 0.2 and β_s = 1.3.