Swift/eBAT6 E_p − L plane for models with no redshift evolution of the luminosity function (a, c) and with strong redshift evolution of the luminosity function (b, d). Top panels (a, b): independent log-normal E_p scenarios; bottom panels (c, d): intrinsic E_p − L correlation scenarios. The predictions for the entire intrinsic LGRB population is shown as grey contours and the predictions for the mock eBAT6 sample are shown in coloured filled contours. The observed eBAT6 sample is shown as coloured scatter points, the 2D Gaussian kernel density estimation shown in Fig. 4 is omitted for clarity. A full description of the observed data points, the side histograms and the dashed, dot-dashed and dotted curves of the figure is presented in Fig. 4.