Spectra of the A and B components (panel a) and their polarization parameters as a function of wavelength (panels b–e). Observed Stokes parameters (panels b and c), the degree of polarization (panel d), and the angle of the polarization plane (panel e) for components A (blue) and B (red) of the Q0957+561 lens are shown. The spectropolarimetric data in panels b–e are binned over 40 Å. The left sides of panels b–e show robust estimates for each parameter in the g-SDSS (left) and r-SDSS (right) bands. The right sides of panels b–e show the distribution of parameter values and their average difference for B minus A.