Pulsars and neutron stars/Pulsars in globular clusters

47 Tucanae
The first two pulsars, PSR B0021-72A and B0021-72B were reported by Ables et al. (1988) and Ables et al. (1989) and had a dispersion measure of 65cm-3pc, but were subsequently shown to be false candidates. This was quickly followed by Manchester et al. (1989) (Manchester et al. 1990) who identified B0021-72C with a period of 5.7ms and a dispersion measure of 25cm-3pc. Manchester et al. (1991) subsequently reported the discovery of a further 10 pulsars in the cluster (ONLY SOME OF THESE SEEM TO BE IN THE CATALGOUE?). Robinson et al. (1995) find another pulsar B0021-72N, but also showed that 47Tuc K was non-existent. They also showed that pulsar J is eclipsed by its companion for about a quarter of the orbital period (and they suggest the same for I). A further 9 pulsars (?) were reported by Freire et al. 2000 and they provide 14 timing solutions. Camilo et al. (2000) report on the discovery of the (?) nine new pulsars and discuss their parameters.

McConnell & Ables (2000) presented continuum radio images (from the Australia Telescope Compact Array) at 1.4 and 1.7GHz and study the radio sources within the central regions of the cluster. They identify 11 sources. This was reported in more detail in McConnell, Deacon & Ables (2001). This work continued by McConnell et al. (2004) who obtained a deep continuum observation and determined the total integrated radio flux from all the pulsars in the core of the globular cluster. They showed that the total 20-cm radio flux from all the pulsars in the cluster is $$2.0 \pm 0.3 {\rm mJy}$$ which implies the size of the observable pulsar population to be < 30 pulsars. More recently Miller-Jones et al. (2015) used deep radio imaging of the cluster and identified an X-ray source X9 as a new black hole candidate.

300 X-ray sources were detected in the globular cluster by Heinke et al. (2005) and they estimate around 25 millisecond pulsars in the cluster (and a total number of neutron stars of ~300).

Friere et al. (2001) reported the detection of ionized intracluster gas by comparing the dispersion measures for pulsars with negative period derivatives (which must lie in the distant half of the cluster) and those in the front of the cluster. They show that the cluster electron density is $$n_e = 0.067 \pm 0.015 {\rm cm}^{-3}$$. Freire et al. (2001) describe the timing solutions for 15 pulsars in the cluster. They obtain the pulsar positions, proper motions (for five of the pulsars) and period derivatives. Freire et al. (2003) provided further results from timing the pulsars. They present pulse profiles in the 20cm band, a timing solution for pulsar S and new proper motions. They also detected a second period derivative for PSR J0024-7204H - which suggests the presence of a third nearby object. They found that pulsar J shows variations of dispersion measure as a function of orbital phase. They discuss the binary orbits in detail.

(see Rasio 2000).