Notes. Parameter values held fixed during the fit are given inside square brackets. We use a constant model to account for differences in normalization between each instrument and fix the constant for NuSTAR/PFMA spectra C_FPMA = 1 in each epoch. For the models slimdz and relxillCp, the redshift of AT2018cow (z = 0.01404) is taken. We find that it is only for Epoch 4 that adding a slim-disk component significantly improves the fit compared to only using a power–law model (Table B.2). Nonetheless, we also test a model of a slim disk alone ("constant*TBabs*slimdz") for Epoch 6, as the source becomes much softer at this epoch compared to previous epochs. The symbol "NC" means the parameter cannot be constrained within the allowed range of values (for θ this is 3° ≤θ ≤ 90° and for a_• this is −0.998 ≤ a_• ≤ 0.998). See Dauser et al. 2014 and García et al. 2014 for detailed descriptions of relxillCp parameters.