Long-term observations of the pulsars in 47 Tucanae. I. A study of four elusive binary systems

TL;DR

This study presents long-term timing observations of four binary pulsars in 47 Tucanae, revealing their orbital parameters and unique characteristics, including a wide, circular orbit for 47 Tuc X and orbital variability for 47 Tuc W.

Contribution

First detailed orbital characterization of four elusive binary pulsars in 47 Tuc, including new measurements and full timing solutions for two systems.

Findings

Determined unknown orbital parameters for 47 Tuc V and X.

Obtained full coherent timing solutions for 47 Tuc W and X.

Discovered 47 Tuc X's wide, circular orbit far from cluster center.

Abstract

For the past couple of decades, the Parkes radio telescope has been regularly observing the millisecond pulsars in 47 Tucanae (47 Tuc). This long-term timing program was designed to address a wide range of scientific issues related to these pulsars and the globular cluster where they are located. In this paper, the first of a series, we address one of these objectives: the characterization of four previously known binary pulsars for which no precise orbital parameters were known, namely 47 Tuc P, V, W and X (pulsars 47 Tuc R and Y are discussed elsewhere). We determined the previously unknown orbital parameters of 47 Tuc V and X and greatly improved those of 47 Tuc P and W. For pulsars W and X we obtained, for the first time, full coherent timing solutions across the whole data span, which allowed a much more detailed characterization of these systems. 47 Tuc W, a well-known tight eclipsing binary pulsar, exhibits a large orbital period variability, as expected for a system of its class. 47 Tuc X turns out to be in a wide, extremely circular, 10.9-day long binary orbit and its position is ~3.8 arcmin away from the cluster center, more than three times the distance of any other pulsar in 47 Tuc. These characteristics make 47 Tuc X a very different object with respect to the other pulsars of the cluster.