Long-term observations of the pulsars in 47 Tucanae – II. Proper motions, accelerations and jerks

Abstract

This paper is the second in a series where we report the results of the long-term timing of the millisecond pulsars (MSPs) in 47 Tucanae with the Parkes 64-m radio telescope. We obtain improved timing parameters that provide additional information for studies of the cluster dynamics: a) the pulsar proper motions yield an estimate of the proper motion of the cluster as a whole ($\mu_{\alpha}\, = \, 5.00\, \pm \, 0.14\, \rm mas \, yr^{-1}$, $\mu_{\delta}\, = \, -2.84\, \pm \, 0.12\, \rm mas \, yr^{-1}$) and the motion of the pulsars relative to each other. b) We measure the second spin-period derivatives caused by the change of the pulsar line-of-sight accelerations; 47 Tuc H, U and possibly J are being affected by nearby objects. c) For ten binary systems we now measure changes in the orbital period caused by their acceleration in the gravitational field of the cluster. From all these measurements, we derive a cluster distance no smaller than $\sim\,$4.69 kpc and show that the characteristics of these MSPs are very similar to their counterparts in the Galactic disk. We find no evidence in favour of an intermediate mass black hole at the centre of the cluster. Finally, we describe the orbital behaviour of the four "black widow" systems. Two of them, 47 Tuc J and O, exhibit orbital variability similar to that observed in other such systems, while for 47 Tuc I and R the orbits seem to be remarkably stable. It appears, therefore, that not all "black widows" have unpredictable orbital behaviour.