χ² map of the LTE slab model fit of SO₂. 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 clearly reveals that the SO₂ emission is optically thin with an excitation temperature of 92 ± 8 K.