SO line temperature ratio T_R(SO 10₁₁−10₁₀)/T_R(SO 9₈−8₇) versus intrinsic line temperature T_R(SO 10₁₁−10₁₀) predicted by RADEX slab models at T_K = 50, 500 K (black and red points/curves). Each curve corresponds to the labelled column density N_SO/ ΔV increasing from 10¹⁵ to 2 × 10¹⁶ cm^-2 (km s^-1)^-1 going from left to right. Each dot along the curves corresponds to the labelled log  (n_H2) (from 10^6.5 to ≥ 10⁸ cm^-3). Models for which the emission in the SO 10₁₁−10₁₀ is optically thin are marked with a cross, optically thick models with a star. The black points indicate the SO line ratio and the SO 10₁₁−10₁₀ line intensity (or their lower/upper limits) corrected for beam dilution in the B2, B3 and R2 knots and in the disk blue and red lobes.