Optical Appearance of the Konoplya–Zhidenko Rotating Non-Kerr Black Hole Surrounded by a Thin Accretion Disk

Abstract

In this study, we investigate the optical appearance of rotating Konoplya–Zhidenko non-Kerr black holes in the presence of thin accretion disks, with the aim of examining whether the information of deformation parameters manifest in observable signatures. By employing a fisheye camera model in conjunction with backward ray-tracing techniques, we simulate images for both prograde and retrograde accretion scenarios. The results indicate that the deformation parameter $\xi$ can partially mitigate the shadow deformation induced by the rotation parameter $a$. The inner shadow displays characteristic morphological transformations at varying observation angles, transitioning from an axisymmetric circular form at low angles to a hat-like configuration at higher angles. Furthermore, at high observational inclination angles, the direct image and the lensed image become distinctly discernible, and an increase in the deformation parameter $\xi$ enhances the observed intensity of the image. Interestingly, the motion behavior of the accretion flow influences the observed intensity distribution on the screen, a finding that is consistent with the redshift distribution. Hence, variations in the deformation parameter $\xi$, the observation angles, and the motion behavior of the accretion flow collectively influence the observable appearance of the black hole. We expect this work to provide valuable references for identifying observable signatures of spacetime deviations from general relativity.