Strong gravitational lensing by a Konoplya-Zhidenko rotating non-Kerr compact object

TL;DR

This paper investigates strong gravitational lensing effects around a novel rotating non-Kerr black hole model, revealing unique lensing signatures and potential observational differences from standard Kerr black holes.

Contribution

It introduces a new rotating non-Kerr black hole metric with a deformation parameter and analyzes its strong lensing properties, highlighting differences from other non-Kerr spacetimes.

Findings

Deflection angle diverges logarithmically near weakly naked singularities.

Finite deflection angle near naked singularities depends on rotation and deformation parameters.

Estimated observable lensing effects for the Milky Way's central object.

Abstract

Konoplya and Zhidenko have proposed recently a rotating non-Kerr black hole metric beyond General Relativity and make an estimate for the possible deviations from the Kerr solution with the data of GW 150914. We here study the strong gravitational lensing in such a rotating non-Kerr spacetime with an extra deformation parameter. We find that the condition of existence of horizons is not inconsistent with that of the marginally circular photon orbit. Moreover, the deflection angle of the light ray near the weakly naked singularity covered by the marginally circular orbit diverges logarithmically in the strong-field limit. In the case of the completely naked singularity, the deflection angle near the singularity tends to a certain finite value, whose sign depends on the rotation parameter and the deformation parameter. These properties of strong gravitational lensing are different from those in the Johannsen-Psaltis rotating non-Kerr spacetime and in the Janis-Newman-Winicour spacetime. Modeling the supermassive central object of the Milk Way Galaxy as a Konoplya-Zhidenko rotating non-Kerr compact object, we estimated the numerical values of observables for the strong gravitational lensing including the time delay between two relativistic images.