Variations of the normalized Stokes parameters q and u with the pulsar phase, averaged over all DUs in the 2–8 keV energy band (beige circles and arrows) for the bright (left) and low (right) states of GRO J1008–57. Each circle corresponds to a specific phase bin, numbered successively following the binning shown in Fig. 4. The circle radius represents the 1σ uncertainty value. The phase-averaged value is shown with a red cross in the corresponding panel.