Polarized image of an equatorial emitting ring around a Konoplya-Zhidenko rotating non-Kerr black hole

TL;DR

This work examines polarized images of an equatorial emitting ring around a Konoplya-Zhidenko rotating non-Kerr black hole, introducing a deformation parameter $\eta$ that extends the Kerr spin bounds and alters the strong-field spacetime. Using an analytic, ring-based radiative transfer framework with a ZAMO frame and the Penrose-Walker constant, the authors trace photon geodesics and compute the observed polarization, exploring how $\eta$, the spin $a$, magnetic-field geometry, fluid velocity, and inclination influence polarization intensity and EVPA. Key findings show that $\eta$ generally reduces polarization for equatorial-field configurations and produces non-monotonic or geometry-dependent EVPA behavior; the Stokes $Q$-$U$ loops and image patterns provide robust signatures of spacetime deformation. The results suggest that high-resolution polarized imaging could serve as a precision probe for deviations from Kerr geometry and tests of general relativity in the strong-field regime, with implications for interpreting EHT-like observations of black holes.

Abstract

We investigate the polarized images of an equatorial emitting ring around a Konoplya-Zhidenko rotating non-Kerr black hole, which introduces an additional deformation parameter. The deformation parameter $η$ allows the spin parameter to extend beyond the bounds imposed by the standard Kerr black hole. The results indicate that the polarized images depend not only on the magnetic field configuration, fluid velocity, and observer inclination angle, but also on the deformation parameter and the spin parameter. As the deformation parameter increases, the polarization intensity decreases monotonically when the magnetic field lies in the equatorial plane, whereas it does not vary monotonically when the magnetic field is perpendicular to the equatorial plane. The variation of the electric vector position angle with the deformation parameter is complex. For a fixed deformation parameter, the polarization intensity exhibits a non-monotonic dependence on the spin parameter and varies with azimuthal angle. We also investigate the impact of the deformation parameter on the Stokes Q-U loops. The imprint of the deformation parameter in polarized images may serve as a high-precision observational probe for detecting deviations of black hole spacetime from the Kerr geometry and testing general relativity.

Figures (10)

• Figure 1: Effects of $a$ on the polarization vectors and EVPA in the Konoplya-Zhidenko rotating non-Kerr black hole\ref{['Metric01']}. Here $r_s=4.5$, $\theta_o=20^{\circ}$, $\beta_\nu=0.3$ and $\chi=-90^{\circ}$.
• Figure 2: Effects of $\eta$ on the polarization vectors and EVPA in the Konoplya-Zhidenko rotating non-Kerr black hole\ref{['Metric01']} for different $a$, with the equatorial magnetic field with only an radial component $B_{r}$. Here $r_s=4.5$, $\theta_o=20^{\circ}$, $\beta_\nu=0.3$ and $\chi=-90^{\circ}$.
• Figure 3: Effects of $\eta$ on the polarization vectors and EVPA in the Konoplya-Zhidenko rotating non-Kerr black hole\ref{['Metric01']} for different $a$, with the equatorial magnetic field with only an azimuthal component $B_{\phi}$. Here $r_s=4.5$, $\theta_o=20^{\circ}$, $\beta_\nu=0.3$ and $\chi=-90^{\circ}$.
• Figure 4: Effects of $\eta$ on the polarization vectors and EVPA in the Konoplya-Zhidenko rotating non-Kerr black hole\ref{['Metric01']} for different $\chi$, with the magnetic field lying in the equatorial plane. Here $r_s=4.5$, $a=0.5$, $\theta_o=20^{\circ}$, $\beta_\nu=0.3$, $B_r=0.87$, $B_\phi=0.5$ and $B_\theta=0$.
• Figure 5: Effects of $\eta$ on the polarization vectors and EVPA in the Konoplya-Zhidenko rotating non-Kerr black hole\ref{['Metric01']} for different observer inclination angle $\theta_o$, with the magnetic field lying in the equatorial plane. Here $r_s=4.5$, $a=0.5$, $\beta_\nu=0.3$, $\chi=-90^{\circ}$, $B_r=0.87$, $B_\phi=0.5$ and $B_\theta=0$.