Analytical study of gravitational lensing in Kerr-Newman black-bounce spacetime

TL;DR

This paper analyzes gravitational lensing in Kerr-Newman black-bounce spacetime, deriving formulas for light deflection angles and Einstein ring sizes, revealing how charge and regularization parameters influence observable lensing features.

Contribution

It provides a new closed-form expression for light deflection angles in Kerr-Newman black-bounce spacetime and studies their impact on Einstein rings and caustic structures.

Findings

Deflection angle increases as charge and regularization parameter decrease.

Charge significantly affects Einstein ring size, while regularization parameter has negligible effect.

Results impact the observational signatures of Kerr-Newman black-bounce objects.

Abstract

We investigate the equatorial deflection angle of light rays propagating in Kerr-Newman black-bounce spacetime. Furthermore, we analyze the light ray trajectories and derive a closed-form formula for deflection angle in terms of elliptic integrals. The deflection angle increases with the decrease of charge and regularisation parameter for a particular impact parameter. We also study the strong field limit of the deflection angle. Using this strong deflection angle formula and lens equation, we find the radius of the first Einstein ring and study its dependence on the charge and the regularisation parameter. We demonstrate that the charge has a robust effect on the size of the Einstein rings, but the effect of the regularization parameter on the ring size is negligible. We also investigate the non-equatorial lensing and the caustic structures for small polar inclination, and the same observations appear to hold. These results directly affect the observational appearance of the Kerr-Newman black-bounce.