Schematic view of the geometry. The left side corresponds to the observer frame ℛ_obs, in which the jet is tilted by angle θ from the line of sight (along x_obs) and is boosted by a Lorentz factor Γ (velocity Σ) along . The minijet is defined by its Lorentz factor γ (velocity β), in the jet frame ℛ_jet (top right). The orientation of the minijet along compared to the jet axis in its rest frame, x_jet, is defined by the spherical angles ψ and ϕ. The emission is assumed isotropic in the minijet frame ℛ_minijet (bottom right).