Shadow, Emission, and Strong-Field Lensing of Dilatonic Black Holes

Abstract

We study the shadow and strong-field optical properties of a static, spherically symmetric dyon-like dilatonic black hole. The photon sphere radius, critical impact parameter, and shadow radius are obtained and analyzed in terms of the charge $Q$ and the dilatonic coupling parameter $a$. We show that increasing these parameters decreases the photon sphere and shadow radii, leading to a smaller apparent shadow. The predicted angular diameter is compared with the observational data for M87${}^{\ast }$ and SgrA${}^{\ast }$, and the model parameters are constrained. We also estimate the high-frequency energy emission rate in the geometric-optics approximation and derive the leading Bozza coefficient $\bar{a}$, which characterizes the logarithmic behavior of the deflection angle in the strong-field regime. Astrophysical implication of the obtained outcomes are discussed.

17 pages, 7 figures