Abstract
Profiles of allowed regions for the propagation of rays in the vicinity of a Kerr black hole in the refractive medium (plasma) are studied. Cold plasma approximation is applied and the dispersion relation in the given surroundings is solved.
Three different plasma density profiles - nonsingular isothermal sphere, exponential, and power-law distributions, corresponding to various lensing galaxy models, are considered. The allowed regions are analyzed in terms of impact parameters, allowing to estimate ray properties favorable for their detection.
It is shown that plasma significantly affects the range of ray impact parameters which can be reached by an observer located between the outer horizon and the static limit of the black hole. It is shown that the plasma effect is most significant close to the black hole and for the power-law density distribution model.