Simulated Athena/X-IFU 15 ks spectrum for a WISSH-like quasar at z = 3.4 with UFO absorber with velocity 0.15c, cm^-2, log (U) = 2.3, and v_turb = 5000 km s^-1 (see Sect. 6.2). The solid line indicates the best-fit baseline continuum model modified by the UFO and the Fe Kα line (the dotted line indicates the baseline continuum component). Absorption lines with observed EW > 1 keV and the Fe Kα emission line are labeled. The inset shows confidence contours for U and . Contours are 68, 90%, and 99% for two interesting parameters.