[Fe K$\alpha$]{} line is likely the sum of a constant component (from distant, Compton-thick material) and a variable one (from Compton-thin material). Concerning the high-energy cut-off, ambiguous results have been reported in literature (see Table \[tab:past\]). [@ricci2017] report a value of [$448^{+ 63}_{- 55}$]{} keV, while [@lubinski2016] report a coronal temperature of [$230^{+ 51}_{- 57}$]{} keV and an optical depth of [$0.52^{+ 0.14}_{- 0.13}$]{}. From 2008-2009 [[*INTEGRAL*]{}]{} data, [@beckmann2010] report a cut-off of $\sim 80$ keV with a hard photon index, but these results are not confirmed by [[*NuSTAR*]{}]{} [@marinucci2015]. Indeed, only lower limits to the high-energy cut-off have been found with [[*NuSTAR*]{}]{} [210 keV: @marinucci2015], [[*Suzaku*]{}]{} [250 keV: @rivers2014] and [[*BeppoSAX*]{}]{} [143 keV: @risaliti2002]. No hard X-ray spectral variability has been detected by [@caballero2012] and [@soldi2014] from BAT data, despite the significant flux variability.

                                         [NGC 4388]{}              [NGC 2110]{}
  ------------------------------- -------------------------- -------------------------
        ${E_{\textrm{c}}}$               [$> 145$]{}                [$> 143$]{}
                                         [$> 180$]{}              [$82 \pm 9$]{}
                                   [$209^{+ 44}_{- 32}$]{}          [$> 250$]{}
             \[0.5ex\]             [$202^{+ 111}_{- 54}$]{}         [$> 210$]{}
                                         [$> 104$]{}          [$448^{+ 63}_{- 55}$]{}
   \[0.5ex\] ${kT_{\textrm{e}}}$    [$53^{+ 17}_{- 9}$]{}     [$230^{+ 51}_{- 57}$]{}
                                                                 [$190 \pm 130$]{}

  : Previous constraints on high-energy cut-off and coronal temperature (both in keV) reported in literature.[]{data-label="tab:past"}

Data selection and reduction {#sec:data}
============================

