Parameters estimation and strong gravitational lensing of nonsingular Kerr-Sen black holes

Abstract

The recent time witnessed a surge of interest in strong gravitational lensing by black holes is due to the Event Horizon Telescope (EHT) results, which suggest comparing the black hole lensing in both general relativity and heterotic string theory. That may help us to assess the phenomenological differences between these models. Motivated by this, we consider gravitational lensing by the nonsingular Kerr-Sen black holes, which encompass Kerr black holes as a particular case, to calculate the light deflection coefficients $p$ and $q$ in strong-field limits, while the former increases with increasing parameters $k$ and charge $b$, later decrease. We also find a decrease in the light deflection angle ${\alpha }_D$, angular position ${\theta }_{\infty }$ decreases more slowly and impact parameter for photon orbits $u_m$ more quickly, but angular separation $s$ increases more rapidly with parameters $b$ and $k$. We compare our results with those for Kerr black holes, and also the formalism is applied to discuss the astrophysical consequences in the case of the supermassive black holes NGC 4649, NGC 1332, Sgr A* and M87*. In turn, we also investigate the shadows of the nonsingular Kerr-Sen black holes and show that they are smaller and more distorted than the corresponding Kerr black holes and nonsingular Kerr black holes shadows. The inferred circularity deviation $\Delta C\le 0.10$, for the M87* black hole shadow, put constraints on the nonsingular Kerr-Sen black hole parameters ($a,k$) and ($a,b$). The maximum shadow angular diameter for $b=0.30M$ and $k=0.30M$ are, respectively, ${\theta }_d=35.3461\mu$as and ${\theta }_d=35.3355\mu$as. We also estimate the parameters associated with nonsingular Kerr-Sen black holes using the shadow observables.

26 pages, 16 figures and 2 tables. Matched with the published version

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• Superradiance evolution of black hole shadows revisited
• No-Hair Theorem in the Wake of Event Horizon Telescope
• Testing Rotating Regular Metrics with EHT Results of Sgr A*
• Testing strong gravitational lensing effects by supermassive compact objects with regular spacetimes
• Investigating effects of dark matter on photon orbits and black hole shadows
• Estimating the cosmological constant from shadows of Kerr--de Sitter black holes
• Testing EGB gravity coupled to bumblebee field and black hole parameter estimation with EHT observations
• Study of light deflection and shadow from a hairy black hole under the influence of the non-magnetic plasma
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