Contour plot of the χ² maps (Eq. (8)) considering T_L, θ_L, which are the two parameters of interest. Solid lines: decrease of likelihood of 1, 3, and 5 σ relative to the hot solution minimum of each epoch (Press et al. 1992). Grey dashed line: temperature profile of a spherically thin shell enclosing a perfect black body (Eq. (9)). Triangles with error bars: cold solutions for both epochs corresponding to the absolute minima. Crosses with error bars: hot solutions for both epochs (corresponding to the local minima).