Abstract
A dilatonic dyonic black hole solution with the gravitational radius \(2\mu\) and two charges \(Q_{1}\) and \(Q_{2}\) (electric and magnetic ones) is considered in a gravitational 4D model with one scalar field and one 2-form, with the dilatonic coupling constant \(\lambda=\pm 1/\sqrt{2}\) . Circular null geodesics are explored. The 3rd order polynomial master equation for the radius \(R_{0}\) of photon sphere is studied. There is only one solution with \(R_{0}>2\mu\) . The circular null geodesics are shown to be unstable. The black hole shadow is studied, and relations for the shadow angle and critical impact parameter are obtained.
