Some properties of the Kerr solution to low energy string theory

The Kerr solution to axidilaton gravity is analyzed in the Debney-Kerr-Schild formalism. It is shown that the Kerr principal null congruence retains its property to be geodesic and shear-free; however, the axidilatonic Kerr solution is not algebraically special; it is of type I in the Petrov-Pirani classification and may not be represented in the Kerr-Schild form. A limiting form of this solution is considered near the ringlike Kerr singularity. This limiting solution is similar to that for the field of fundamental heterotic string obtained by Sen.