Radiative transfer modelling of the HNCO (4–3) emission. We demonstrate the likelihood of achieving the observed intensities (1 to 5 K) from a grid of models. This plot shows contours at the 10, 25, 50, 75, 90, and 95 per cent likelihoods of achieving the observed brightness temperatures, through varying the T_kin, line width, and HNCO abundance. On the upper y-axis, we show the predicted depth calculated from the column and number densities $(L=N_{{\mathrm{H}}_2}/n_{{\mathrm{H}}_2})$. The vertical dashed lines show the angular resolution of the observations and the measured size of the ring-like structure, which we use as upper and lower bounds to constrain the parameter space. We find a peak likelihood of $n_{{\mathrm{H}}_2}\approx {10}^{4.2}{\mathrm{c}\mathrm{m}}^{-3}$, with a large spread in plausible densities between 10^3.5 and 10^5.5 cm⁻³.