Average polarization in the 2−8 keV energy band for the pre-dip (dashed blue lines) and post-dip (dashed green lines) of the first observation of GX 13+1, and for the new observation (solid dark red lines). Contours correspond to the 68% and 99% CLs. A significant detection of polarization at 5.2σ is obtained in the new observation with the PA aligned with the post-dip reported in B24.