Finding chart covering the 4′ × 3′ field of GRB 071028B as observed with GROND for 2.22 h in the r′ band during the first observing night. The circle represents the astrometrically corrected Swift/XRT position with its 90% error radius. All secondary standard stars used for the photometric calibration (see Table 2), the afterglow (A), and a putative foreground galaxy (G) are labelled. A scale-up of the afterglow area is shown in the bottom panel.