Contour plots for the logarithmic electron density (log N) and the iron abundance of the disk obtained applying model 4 to October and April 16 data (left panel) and April 15 data (right panel). The contours represent the 1σ, 2σ, and 3σ confidence levels, and the cross marks the best-fit values obtained from the best fit. The axis limits have been rescaled for visual purposes.