Symmetries of asymptotically flat electrovacuum space-times and radiation

Symmetries compatible with asymptotic flatness and admitting gravitational and electromagnetic radiation are studied by using the Bondi-Sachs-van der Burg formalism. It is shown that in axially symmetric electrovacuum space-t imes in which at least locally a smooth null infinity in the sense of Penro se exists, the only second allowable symmetry is either the translational s ymmetry or the boost symmetry. Translationally invariant space-times with, in general, a straight "cosmic string'' along the axis of symmetry are nonr adiative although they can have a nonvanishing news function. The boost-rot ation symmetric space-times are radiative. They describe "uniformly acceler ated charged particles'' or black holes which in general may also be rotati ng - the axial and an additional Killing vector are not assumed to be hyper surface orthogonal. The general functional forms of both gravitational and electromagnetic news functions, and of the mass aspect and total mass of as ymptotically flat boost-rotation symmetric space-times at null infinity are obtained. The expressions for the mass are new even in the case of vacuum boost-rotation symmetric space-times with hypersurface orthogonal Killing v ectors. In the Appendices some errors appearing in previous works are corre cted. (C) 1998 American Institute of Physics. [S0022-2488(98)00311- 9].