Illustration of the correlation between ψ and PA for photospheric emission models. Left: illustration of the photospheric emission when observing the GRB with ι > 0° and ψ = 0°. The observed area with a size of 1/Γ is in gray and is no longer fully contained in the beam allowing for PD > 0. The polarization of the remaining emission areas no longer cancels out, and the PA is aligned with ψ. Right: the same as left but now with ψ = 45° resulting in a PA of 45°.