Analysis of the SiO line blue- and red-shifted emissions towards A1 as observed with VLA and SMA (convolved to the angular resolution of the VLA image). The solutions for the observed SiO(1–0) and SiO(5–4) brightness temperatures (solid lines) at the typical red- (+116 km s^-1) and blue-shifted (+106 km s^-1) velocities are shown in the n_H2–N(SiO) plane for non-LTE (RADEX) plane-parallel models at the labelled kinetic temperatures. Dashed lines are for the uncertainties. The SiO(5–4) brightness temperatures are 4.4 K (+116 km s^-1) and 4.3 K (+106 km s^-1), while the SiO(1–0) brightness temperature is 4.0 K (+116 km s^-1). Given the blue-shifted absorption observed towards A1, we plot in black the solutions corresponding to the derived SiO(1–0) excitation temperature (≃ 6 K, see Sect. 4.1).