Core collapse in very massive stars can lead to a cerntral black hole that swallows the rest of the star and in less massive stars to a central neutron star and explosion. There is probably an intermediate mass range that gives an explosion and a central black hole; supernova remnants with no observable central object are candidates. The association of pulsars with Type II supernovae gives an estimate of the pulsar power to be expected in a supernova, but the uncertainty in the initial pulsar periods gives a wide range in possible powers. The relativistic wind bubble model for the Crab Nebula has steadily developed and there are now predictions regarding particle acceleration in the optical wisps. The bubble model with expansion into supernova gas can also be applied to other young pulsar nebulae.

Introduction

The study of compact objects in supernova remnants has long been troubled by the lack of evidence for such objects. For many years, the Crab and Vela pulsars were the only compact objects observed in remnants. More recently, the number of pulsar/remnant associations has increased to 9 or 10 (Kaspi et al. 1992; Kulkarni et al. 1993). In other cases, the presence of a pulsar is inferred from a centrally condensed, flat radio spectrum nebula thought to be created by a pulsar. The study of these objects, as well as more detailed study of the Crab Nebula, has led to a general theoretical picture, although many basic uncertainties remain.