Jet viewing angle ϕ versus intrinsic jet speed β. The blue solid curve shows the lower limit of the β–ϕ relation derived from the constraint J ≳ 2.92, and the other solid curves (red, orange, green, purple, and black) correspond to Doppler factors ranging from 1 to 10. The shaded region represents the allowed parameter space satisfying the constraints on ϕ and β, i.e., J ≳ 2.92 and δ ∼ 1 (δ < 2).