  An exact heterotic string theory on an AdS2xS2 background supported by an
electromagnetic flux is found as a marginal deformation of an SL(2,R)xSU(2) WZW
model. Based on a talk given at NATO Advanced Study Institute and EC Summer
School on String Theory: from Gauge Interactions to Cosmology, Cargese,
Corsica, France, 7 Jun - 19 Jun 2004.
