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

Ridolfi, A.

Member of the Collaboration Group

;Freire, P. C. C.

Member of the Collaboration Group

;Torne, P.

Member of the Collaboration Group

;Heinke, C. O.

Member of the Collaboration Group

;van den Berg, M.

Member of the Collaboration Group

;Jordan, C.

Member of the Collaboration Group

;Kramer, M.

Member of the Collaboration Group

;Bassa, C. G.

Member of the Collaboration Group

;Sarkissian, J.

Member of the Collaboration Group

;D'Amico, N.

Member of the Collaboration Group

;Lorimer, D.

Member of the Collaboration Group

;Camilo, F.

Member of the Collaboration Group

;Manchester, R. N.

Member of the Collaboration Group

;Lyne, A.

Member of the Collaboration Group

2016-01-01

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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 programme 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-d long binary orbit and its position is ~3.8 arcmin away from the cluster centre, 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.