X-ray spectra fitted with the absorbed disc black body plus power-law model described in the text. Data were rebinned to reach a 5σ significance or by a factor of 5 for plotting purposes. In the upper panel black, red, and green (filled circles) data refer to ROSAT spectra (first, second, and third observations, respectively). Blue (open circles) data refer to the Chandra spectrum. Light blue, magenta, and orange (filled stars) to Swift spectra (first, second, and third observations, respectively). In the lower panel residuals in terms of χ are plotted with the same colour codings and symbols.