Preferred model: spectra of SiO ν= 0J = 5−4 at various positions. The black histogram is the observed spectrum at the centre of continuum, green, blue, cyan, and magenta histograms are the observed spectra along the eastern, southern, western, and northern legs, respectively, at various offset radial distances as indicated in each panel. The red curves are the modelled spectra predicted by ratran. Our model does not produce the population inversion (i.e. negative excitation temperature) required for maser emission in this SiO transition, so we do not expect our modelled spectra to show any maser emission, as seen in the spike in the upper right panel (see text for the discussion of the spike).