Complex Structure of Kerr Geometry and Rotating `Photon Rocket'   Solutions
  In the frame of the Kerr-Schild approach, we obtain a generalization of the Kerr solution to a nonstationary case corresponding to a rotating source moving with arbitrary acceleration. Similar to the Kerr solution, the solutions obtained have the geodesic and shear free principal null congruence. The current parameters of the solutions are determined by a complex retarded-time construction via a given complex worldline of source. The real part of the complex worldline defines the values of the boost and acceleration while the imaginary part controls the rotation. The acceleration of the source is accompanied by a lightlike radiation along the principal null congruence. The solutions obtained generalize to the rotating case the known Kinnersley class of the "photon rocket" solutions. 
Alexander Burinskii