092116

We propose to observe the Seyfert galaxy NGC 4151 with XMM-Newton (50 ks) and NuSTAR (100 ks) simultaneously to the scheduled IXPE (Imaging X-ray Polarimeter Explorer) pointing. Accurate measurements of the hot corona parameters have been reported but no significant constraints on the coronal geometry (slab sphere semi-sphere) have been possible so far. X-ray polarimetry has the potentiality to provide such constraints but the signal is partly degenerate with respect to the geometrical and physical parameters of the accretion disk-corona system. To reduce them and constrain the geometrical shape of the corona simultaneous and independent constraints on coronal temperature and optical depth strength of the reflection components provided by a joint XMM-Newton and NuSTAR observation are vital. [truncated! Please see actual data for full text]