The broad-band fit

Next, we included the [[*XMM–Newton*]{}]{} and [[*NuSTAR*]{}]{} data. We first fitted the data with a phenomenological model consisting of an absorbed cut-off power law plus a Gaussian [Fe K$\alpha$]{} line. In [[xspec]{}]{}, the model reads <span style="font-variant:small-caps;">phabs(cutoffpl+zgauss)</span>. According to the results of [@marinucci2015], the flux of the iron line varies among the [[*XMM–Newton*]{}]{} and the two [[*NuSTAR*]{}]{} observations, while the values of the line energy and intrinsic width are consistent with each other within the errors. We thus left the line flux free to vary among the observations, while the intrinsic width was tied. Keeping all the other parameters tied among the different spectra, we found a good fit (${\chi^{2}/\textrm{dof}}=975/1009$). However, we found an improvement by leaving the absorbing column density free to vary among the spectra, finally obtaining ${\chi^{2}/\textrm{dof}}=947/1007$ (${\Delta \chi^{2}}/{\Delta \textrm{dof}}= -28/-2$; the probability of chance improvement is [$ 4 \times 10^{-7}$]{} from an F-test), with $\Gamma \simeq 1.65$ and a ${E_{\textrm{c}}}= {320^{+ 100}_{- 60}}$ keV. No significant improvement is found by leaving the photon index free to vary, and the cut-off energy is consistent with the value reported above. The best-fitting parameters are reported in Table \[tab:fits\_2110\], while the contour plots of the cut-off 