Light curve (upper panel) and hardness-ratio light curves (lower panel) extracted from the whole XMM-Newton observation set. The time bin-size in both panels is 1000 s to make the plots clearer. The vertical dotted lines and the related labels indicate the time gap between one observation and the next. We plot in red the data corresponding to the occultation events presented in Risaliti et al. (2011) (see text for discussion). The time is measured from the beginning of the XMM-Newton mission.