  Spacetimes generated by a lightlike particle source for topologically massive
gravity and its limits - Einstein gravity and the pure gravitational
Chern-Simons model - are obtained both by solving the field equations and by
infinite boosts of static metrics. The resulting geometries are the first known
solutions of topologically massive gravity that are asymptotically flat and
generated by compact matter sources. Explicit metrics describing various
multiphoton solutions are also derived. For Einstein gravity, we also construct
such solutions by null boost identifications of Minkowski space and thereby
obtain limits on the energies of the sources.
