Lensing Properties of Lightlike Current Carrying Cosmic Strings

The lensing properties of superconducting cosmic strings endowed with a time dependent pulse of lightlike current are investigated. The metric outside the core of the string belongs to the pp–wave class, with a deficit angle. We study the field theoretic bosonic Witten model coupled to gravity, and we show that the full metric (both outside and inside the core) is a Taub-KerrShild generalization of that for the static string with no current. It is shown that the double image due to the deficit angle evolves in an unambiguous way as a pulse of lightlike current passes between the source and the observer. Observational consequences of this signature of the existence of cosmic strings are briefly discussed. PACS Numbers: 98.80.Cq, 11.17.+y, 12.15.Cc Typeset using REVTEX