Kerr-Sen dilaton-axion black hole lensing in the strong deflection limit

TL;DR

This paper investigates the strong deflection gravitational lensing effects of Kerr-Sen dilaton-axion black holes, revealing how their unique properties influence relativistic image formation and caustic structures.

Contribution

It provides a numerical analysis of quasi-equatorial lensing by Kerr-Sen black holes, highlighting the caustic drift and the impact of charge and angular momentum on lensing features.

Findings

Caustics drift away from the optical axis and shift clockwise.

Critical curves decrease with increasing charge parameter.

Lensing characteristics differ from Schwarzschild, Kerr, and Gibbons-Maeda black holes.

Abstract

In the present work we study numerically quasi-equatorial lensing by the charged, stationary, axially-symmetric Kerr-Sen dilaton-axion black hole in the strong deflection limit. In this approximation we compute the magnification and the positions of the relativistic images. The most outstanding effect is that the Kerr-Sen black hole caustics drift away from the optical axis and shift in clockwise direction with respect to the Kerr caustics. The intersections of the critical curves on the equatorial plane as a function of the black hole angular momentum are found, and it is shown that they decrease with the increase of the parameter $Q^{2}/M$. All of the lensing quantities are compared to particular cases as Schwarzschild, Kerr and Gibbons-Maeda black holes.