Position–velocity diagrams of the CO and SO emission along the jet main axis (see Fig. 1). Top: CO 2–1 as observed at 1″ with the IRAM interferometer. The different knots identified close to the protostar are indicated. The best-fitting relation to the gas acceleration |V – V_lsr|/V₀ = exp(−δ₀/δ) is superimposed in cyan. Middle: Magnified view of the CO 2–1 emission in the central protostellar region near Cep E-A. Bottom: SO N_J = 5₄–4₃ as observed at 0.4″ resolution with NOEMA. The first contour and the contour interval are 10% and 15% of the peak intensity, respectively. The dashed red lines mark the ambient cloud velocity (V_lsr = −10.9 km s⁻¹). The velocity resolution of the CO and SO observations is 3.3 km s⁻¹ and 2.8 km s⁻¹, respectively. Fluxes are expressed in Jy beam⁻¹.