Self-Dual Dyon in Dilaton-Axion Gravity

A class of backgrounds invariant under inversion of the Ernst matrix potential is identified with the SU(2)/U(1) subspace of target space of the stationary D = 4 low energy heterotic string theory. It is shown that the general spherically symmetric solution possesses the U(1) symmetry related to electromagnetic duality and describes a naked dyon singular at the point of charge location.