Best-fit model to the first observation of the Crab pulsar by IXPE in the 2 − 4 keV range. The data reduction was performed with the IXPEOBSSIM package considering equipopulated binning for the Stokes parameters (first panel), and for the polarization degree (second panel) and polarization angle (third panel). The green line in the second panel corresponds to MDP₉₉. The solid gray lines in the first three panels correspond to the best-fit model without a phase shift. The orange and gray arrows highlight the polarization angle swing at the interpulse with and without a phase shift, respectively. For completeness, we include the pulse profile with 400 equispaced bins (fourth panel).