Upper panels: soft (0.3–0.7 keV) vs. hard (2–10 keV) , computed within the 80 ks (left), and 40 ks (right) intervals. Lower panels: similar plots for in the 0.7–2 vs. in the 2–10 keV band. The best fit curves are plotted with solid lines and the combined 1-σ error on the slope and normalisation with dotted lines. The red dashed lines represents the one to one relations expected in the case of achromatic variations. On top of each panel (in this and all similar subsequent figures) we report the best fit models (see also Table 5).