  Near ultraviolet observations of WASP-12b have revealed an early ingress
compared to the optical transit lightcurve. This has been interpreted as due to
the presence of a magnetospheric bow shock which forms when the relative
velocity of the planetary and stellar material is supersonic. We aim to
reproduce this observed early ingress by modelling the stellar wind (or coronal
plasma) in order to derive the speed and density of the material at the
planetary orbital radius. From this we determine the orientation of the shock
and the density of compressed plasma behind it. With this model for the density
structure surrounding the planet we perform Monte Carlo radiation transfer
simulations of the near UV transits of WASP-12b with and without a bow shock.
We find that we can reproduce the transit lightcurves with a wide range of
plasma temperatures, shock geometries and optical depths. Our results support
the hypothesis that a bow shock could explain the observed early ingress.
