PSR J0024–7204ai: A massive eccentric binary system in the globular cluster 47 Tucanae

In this paper we present PSR J0024−7204ai, a 13.026-ms binary pulsar recently discovered in the globular cluster 47 Tucanae by the MeerKAT radio telescope. This is the slowest-spinning pulsar known in this globular cluster. It has a ∼1.67-day orbit with an eccentricity of e ≈ 0.18. Although it is not yet possible to derive an unambiguous phase-connected timing solution, by combining detections obtained from MeerKAT and archival Parkes data, we were able to measure the rate of advance of periastron to a high significance: $ \dot{\omega} = 0.1601 \pm 0.0046 $ deg yr−1. This value implies a total system mass of 2.41 ± 0.11 M⊙ (68.3% C.L.), which, when combined with the binary mass function, gives a maximum pulsar mass of ∼1.7 M⊙ and a minimum companion mass of ∼0.7 M⊙. Apart from being the slowest pulsar in 47 Tucanae, its orbit is by far the most eccentric, and its companion is the most massive among all known binary pulsars in this globular cluster. It is possible that the system is an old millisecond pulsar–carbon-oxygen white dwarf binary whose orbit was perturbed by stellar dynamical interactions in the cluster core. Further follow-up observations of this system will be essential to obtaining a more detailed characterisation of this system and its evolution.