Millisecond pulsars in the globular cluster 47 Tucanae

Searches for pulsars in globular clusters during the past few years have discovered more than 30 pulsars in 13 clusters. About one-third of these are located in the globular cluster 47 Tucanae (NGC 104), and were discovered using the Parkes radio telescope in Australia at an observing frequency of 640 MHz (Manchester et al.). We have made further observations of 47 Tucanae at 640 and 436 MHz, with the aim of searching for previously undiscovered pulsars and performing timing measurements on the known ones. Here we report the discovery at 436 MHz of the pulsar 47 Tuc N, but find that 47 Tuc K, earlier reported by Manchester et al., is non-existent. We present timing solutions for the solitary pulsars 47 Tuc C and D. Both pulsars are found to have negative period derivatives which allow us to put a lower limit on the central density of the cluster. We give improved orbital solutions for the binary pulsars of 47 Tuc E and J, and show that 47 Tuc J is eclipsed by its companion for about a quarter of the orbital period. A preliminary orbital solution is obtained for the binary pulsar 47 Tuc I, which is probably also eclipsing. Finally, we discuss the origin and evolution of the 47 Tucanae pulsars.