Top: distribution of the sources in the z−L_X plane. Positions of four different flux bins in the z−L_X plane are clearly distinguishable as parallel stripes. Different colours represent different average flux bins. Bottom: ΔΓ−Δlog F_S plots for the same four flux bins, drawing the linear fit lines for each bin. The slope, which is the opposite of β, decreases for increasing fluxes. The correlation coefficients are approximately 0.3 and are reported in Table 2. All probabilities of obtaining such correlations by chance are p( >r) < 10^-10.