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Symmetries compatible with asymptotic flatness and admitting gravitationaland electromagnetic radiation are studied by using the Bondi-Sachs-van der Burgformalism. It is shown that in axially symmetric electrovacuum spacetimes inwhich at least locally a smooth null infinity in the sense of Penrose exists,the only second allowable symmetry is either the translational symmetry or theboost symmetry. Translationally invariant spacetimes with in general a straight"cosmic string" along the axis of symmetry are non-radiative although they canhave a non-vanishing news function. The boost-rotation symmetric spacetimes areradiative. They describe "uniformly accelerated charged particles" or blackholes which in general may also be rotating - the axial and an additionalKilling vector are not assumed to be hypersurface orthogonal. The generalfunctional forms of both gravitational and electromagnetic news functions, andof the mass aspect and total mass of asymptotically flat boost-rotationsymmetric spacetimes at null infinity are obtained. The expressions for themass are new even in the case of vacuum boost-rotation symmetric spacetimeswith hypersurface orthogonal Killing vectors. In Appendices some errorsappearing in previous works are corrected.Comment: 23 pages, RevTeX, to appear in JM

Symmetries of asymptotically flat electrovacuum space–times and radiation