Heena Ali, Sushant G. Ghosh
Abstract We investigate the shadow of Kerr-Bertotti-Robinson black holes (KBRBHs), which have a deviation parameter B that captures the effect of an external magnetic field on the spacetime geometry. These spacetimes of Petrov type D are asymptotically non-flat. We utilise the separability of the Hamilton-Jacobi equation to generate null geodesics and examine the crucial impact parameters for unstable photon orbits that define the black hole shadow. We carefully investigate how the magnetic field strength B and spin parameter a influence black hole shadows, discovering that increasing B increases the shadow size while also introducing additional distortions, especially at high spins. We calculate the shadow observables, viz., area A and oblateness D and create contour plots in the parameter space ( a , B ) to facilitate parameter estimation. We also investigate the dependence of the shadow on the observer's position, specifically by altering the radial coordinate r O and the inclination angle θ . For far viewers, the shadow approaches its asymptotic shape, but finite-distance observers perceive substantial deviations. The energy emission rate analysis reveals that the magnetic field parameter B modifies the Hawking radiation spectrum, with increasing B suppressing emission via backreaction, which lowers the Hawking temperature. Our findings confirm that KBRBH shadows encode imprints of magnetic deviations, thereby offering a potential avenue to distinguish Kerr from non-Kerr spacetimes and to probe magnetic effects in the strong-gravity regime.