99% χ² contours (solid black lines) between T_soft and its normalisation for sources showing a positive L–T correlation. For each source, two to four different epochs are represented with the epoch indicated next to the contour. A clear anti-correlation is seen in all cases that closely follows the best-fit values from all the epochs (blue datapoints, 90% confidence level error bars), which indicates that the L–T positive correlation is due to the degeneracy between these two parameters. For the sake of readability, we have ignored epoch 2004-06-05 in the panel of NGC 1313 X-1 as it had a much higher normalisation (∼51) compared to the other observations.