Null limits of generalised Bonnor-Swaminarayan solutions

The Bonnor-Swaminarayan solutions are boost-rotation symmetric space-times which describe the motion of pairs of accelerating panicles which are possi bly connected to strings (struts). In an explicit and unified form we prese nt a generalised class of such solutions with a few new observations. We th en investigate the possible limits in which the accelerations become unboun ded. The resulting space-times represent spherical impulsive gravitational waves with snapping or expanding cosmic strings. We also obtain an exact so lution for a snapping string of finite length.