Upper panel: luminosity–temperature relation with the best-fitting models. The light blue circles show the XXL-C1-GC clusters; the best-fitting model (including selection effects) is shown by the solid black line, the 1σ uncertainty represented by the grey shaded region. The best-fitting model fitted to the data using the BCES regression is shown as the dashed line. Bottom panel: evolution of the luminosity–temperature relation for XXL-C1-GC. The XXL-C1-GC clusters are represented by the light blue circles and the best-fitting model is given by the black solid line; the grey shaded region highlights the 1σ uncertainty.The “strong” and “weak” self-similar expectations are given by the red dashed and blue dashed lines, respectively.