χ² map for SO₂ derived from pure rotational lines in the ALMA data. The χ² values are inversely normalized by the minimum χ² and shown in color. The 1, 2, and 3σ confidence intervals are presented as the black contours. The best-fitting emitting radius, R (in au), is represented by the white contours and is calculated for each grid point by minimizing the χ² assuming a circular emitting area of πR². The χ² map indicates that the SO₂ emission has an excitation temperature of 104 ± 5 K and is marginally optically thick (τ ~ 0.1) with an emitting area of ~ 85 au in radius.