Illustration of the LOS integration. The pulsar in the centre is surrounded by a region with no emission, up to the shock radius r_s (dark shaded region). We assume non-zero emission until the maximum radius of the nebula at r₀. Here we illustrate two exemplary lines of sight s₁ and s₂ at angular offsets θ₁ and θ₂ with respect to the centre (dashed lines). s₁ represents a line which intersects the shock whereas s₂ does not. We integrate the emissivity j_ν along the parts of the lines that are marked in solid orange. Because of the radial symmetry of our model, these parts contain exactly half of the emission expected from the full LOS.