Stokes parameters as a function of energy for IXPE Obs. 1 and Obs. 2 (left panels) and for the combined data set (right panels) obtained with IXPEOBSSIM. The normalized Stokes q parameter is compatible with a constant value in each of the IXPE observations, whereas the Stokes u parameter is not (see Table 3). This behavior of the Stokes parameters is consistent with a variation in PA (see Fig. 4).