Polarized image of an equatorial emitting ring around a 4D Gauss-Bonnet
  black hole
  We have studied the polarized image of an equatorial emitting ring around a
4D Gauss-Bonnet black hole. Our results show that the effects of Gauss-Bonnet
parameter on the polarized image depends on the magnetic field configuration,
the observation inclination angle, and the fluid velocity in the disk. For the
case with pure equatorial magnetic field, the observed polarization intensity
increases with Gauss-Bonnet parameter as the observation inclination angle is
small, but this monotonicity gradually disappears with the increase of the
inclination angle. However, in the case where the magnetic field is vertical to
the equatorial plane, the polarization intensity is an increasing function of
Gauss-Bonnet parameter as the inclination angle is large. The changes of the
electric vector position angle (EVPA) with Gauss-Bonnet parameter in both cases
are more complicated. We also probe the effects of Gauss-Bonnet parameter on
the Strokes $Q$-$U$ loops.
