Shadows of rotating Einstein-Maxwell-dilaton black holes surrounded by a plasma

Abstract

We consider rotating charged black holes with a scalar dilaton field and surrounded by plasma, with the purpose of studying their shadows. The corresponding metric has been previously obtained in the literature from the static solution by using the Newman-Janis algorithm. Assuming a well-known form for the pressureless and nonmagnetized plasma distribution, which is suitable for the separation of the Hamilton-Jacobi equation for light, we derive an expression that determines the shape of the shadow. We present some examples of contours and we analyze their observable properties as functions of the charge and the dilaton coupling. We find that the presence of plasma introduces a dependency on the frequency, with the shadow becoming smaller as the frequency decreases.