exponential cut-off model. The high-energy cut-off has been also observed in other ULXs (e.g., @2006ApJ...641L.125D, [-@2010MNRAS.407..291D]; @2006MNRAS.368..397S; ; @2009MNRAS.397.1836G; @2013MNRAS.435.1758S) and is well described by thermal Comptonization of hot coronal electrons by soft photons (e.g., @1994ApJ...434..570T; @1995ApJ...449..188H). We thus test if a Comptonization model (*wabs\*comptt*) is able to fit the data (Fig. \[figSwift\], bottom). We find that the *Swift* spectrum is well described ($\chi^{2}$/dof=35.01/32) with a Comptonization model of input soft photon temperature $T_\mathrm{0}<$ 0.1 keV and plasma temperature $kT_\mathrm{e}$=1.2 keV (see Table \[specfit\]). The S/N is insufficient for us to detect any contribution from the disk, although the disk should still be present.

Both the *diskbb*, *pow\*highe*, and *comptt* models provide significant improved statistics with respect to the *pow* model, as indicated by the $\chi^{2}$/dof. The Bayesian Information Criterion (BIC; @schwarzBIC; @Kass1995) can be also used as a further indicator of the statistical improvement of one model over another. The BIC value can be calculated as BIC = 2log($L_\mathrm{1}$) - 2log($L_\mathrm{2}$) - ($k_\mathrm{1} - k_\mathrm{2}$)log(n), where $L$ = exp$(-\chi^{2}$/2) for models 1 and 2, respectively, $k$ = number of parameters in model, and $n$ = number of data points. We obtain BIC values in the range 2–6 for the 