  We have performed several simulations in order to test the scientific
capabilities of the IXO calorimeter, with particular emphasis on the detection
of absorption lines in the 3-11keV band. We derived the flux limits for their
detection on several time-scales, compared different response matrices
available and simulated realistic spectra from photo-ionized warm absorbers in
AGNs. This study illustrates the considerable improvements that this instrument
will bring to high resolution spectroscopy, especially related to the study of
accretion and outflows in the central regions of AGNs.
