Peak polarized intensity (left panels) and rotation measure of the peak polarized intensity (right panels). Upper row: WSRT 92 cm data. Lower row: LOFAR 2 m data. The bright rings centered on 18h21m20.ˢ8, +39°42′45″ in the 92 cm data are due to imperfect subtraction of the bright quasar 4C+39.56. Black ellipses in the insets (white background) show the beam size. The location of J1819+3845 is shown with a filled cyan circle.