Spectra and best-fit models of the PN detector acquired during the first XMM-Newton exposure (red symbols) and the third exposure (black symbols). Lower panel: residuals (data – model values). The model for both spectra is an absorbed thermal APEC component plus a Gaussian to take into account the fluorescent emission from partially ionized Fe lines at 6.4 − 6.5 keV. The difference between the two spectra is due to a difference of EM.