Aperture bolometric luminosities, L_{ap,   bol}, plotted against the 2XMMi-DR3 catalogue luminosities, L_{cat,   0.5−2.0}, of the cluster sample with reliable parameters from the spectral fits. The one-to-one relationship is represented by the solid line. The dashed line represents the best-fit using the BCES orthogonal regression method after excluding 12 outliers that are represented by red dots.