Einstein-Maxwell gravitational instantons and five dimensional solitonic   strings
  We study various aspects of four dimensional Einstein-Maxwell multicentred gravitational instantons. These are half-BPS Riemannian backgrounds of minimal N=2 supergravity, asymptotic to R^4, R^3 x S^1 or AdS_2 x S^2. Unlike for the Gibbons-Hawking solutions, the topology is not restricted by boundary conditions. We discuss the classical metric on the instanton moduli space. One class of these solutions may be lifted to causal and regular multi `solitonic strings', without horizons, of 4+1 dimensional N=2 supergravity, carrying null momentum. 
Maciej Dunajski and Sean A. Hartnoll