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Bijendra Kumar Vishvakarma

Publications and source records attributed to Bijendra Kumar Vishvakarma.

4 recordsLinked to original sources

Strong Gravitational Lensing by a Black Hole with a Global Monopole in Kalb-Ramond Bumblebee Gravity

We investigate the strong gravitational lensing and shadow properties of the black hole in the context of bumblebee gravity, characterized by a global monopole charge $κη^2$ and a Lorentz symmetry breaking parameter $γ$. We compute the deflection angles of light passing near the black hole in strong deflection limit, and estimate key lensing observables, including relativistic Einstein rings, absolute magnifications, image separations, and flux ratios, for astrophysical black holes. The black hole shadow is analyzed using the apparent angular size $θ_{\rm Shadow} = 2\,θ_{\infty}$ in the limiting photon orbit. Furthermore, we study the modification of the shadow structure in the presence of a radially infalling, optically thin accretion flow within a generalized framework. Our results indicate that both the global monopole charge and Lorentz-violating parameters significantly influence the photon sphere, lensing observables, and shadow morphology, potentially providing observational signatures for testing bumblebee gravity in the strong-field regime.

gr-qc

Strong Gravitational Lensing by Bardeen Black Hole in Cloud of Strings

We investigate the gravitational lensing by Bardeen black hole in cloud of strings (CoS) in strong field limit. The effect of CoS parameter $b$ has been outlined in comparison with Bardeen black hole lens. The strong deflection limit coefficients are determined in terms of impact parameter for various values of CoS parameter. We obtain magnification of relativistic images and determine relativistic Einstein rings by using the parameters of two astrophysical black hole lenses $SgrA^{*}$ and $M87^{*}$. We constrain CoS parameter of Bardeen black hole using EHT observations for these black holes.

gr-qc

Parameter estimation of the Bardeen-Kerr black hole in cloud of strings using shadow analysis

We consider the rotating generalization of the Bardeen black hole solution in the presence of cloud of strings (CoS). The parameter space for which the black hole horizon exists is determined. We also study the static limit surface and the ergo-region in the presence of the CoS parameter. We consider photon orbits and obtain the deformation of black hole shadows due to rotation for various values of CoS parameter. The shadow deformation is used to determine the black hole spin for different values of the black hole parameters.

gr-qc

Shadows and quasinormal modes of the Bardeen black hole in cloud of strings

We investigate the black hole (BH) solution of the Einstein's gravity coupled with non-linear electrodynamics (NED) source in the background of a cloud of strings. We analyze the horizon structure of the obtained BH solution. The optical features of the BH are explored. The photon radius and shadows of the BH are obtained as a function of black hole parameters. We observe that the size of the shadow image is bigger than its horizon radius and photon sphere. We also study the Quasinormal modes (QNM) using WKB formula for this black hole. The dependence of shadow radius and QN modes on black hole parameters reflects that they are mimicker to each other.

gr-qc