Fit spectral model parameters, kept free for all data groups, and MCMC verification results for data groups before the variation (GR I, upper panel), and at the brightest stage (GR II, lower panel) of RX J0720.4−3125. Derived probability density functions of the basic parameters of the fit model are presented in the diagonal. The lower triangular part depicts samplings from the posteriors of two parameters, whereas the upper one depicts their mutual correlations.