Hitting the Pulsar Jackpot in Terzan 5 with the GBT

We report the discovery of at least 17 new pulsars in the rich globular cluster Terzan 5 using the GBT at 2 GHz. This cluster, located near the galactic center, has long been suspected of harboring many millisecond pulsars (MSPs) due both to its large predicted stellar interaction rate and the steep-spectrum radio emission observed in its core. However, earlier pulsar searches using the Parkes radio-telescope had only uncovered 3 pulsars, due primarily to the deleterious effects of the ISM towards the cluster.

Our single 6-hr observation of Terzan 5 taken in July 2004, resulted in 14 new millisecond and/or binary pulsars, while follow-up observations provided (at least) 3 others. These discoveries imply that the 20+ known pulsars in the cluster are but the tip of the iceberg, and in fact much searching remains to be done with our current data. These discoveries confirm that Terzan 5 is one of the largest producers of MSPs among the Galactic globular clusters.

At least 9 of the new pulsars are members of binary systems. There are two or more eclipsing systems, the 3rd and 4th fastest known rotators, a rare long orbital period (Porb ∼60 days) binary, and two highly eccentric binaries. Timing of these latter systems over the next year will provide their total masses and may (after several years) allow us to separate out the pulsar and companion masses. Two or three of the binaries may have main sequence companions, implying they were formed during exchange encounters after the MSPs were recycled and making them amenable to detection in the near-IR. Timing observations of the ensemble of pulsars will allow us to probe the mass-to-light ratio of the cluster core (and provide evidence for or against a black hole residing there), the mass distribution of the cluster as projected on the sky, and other aspects of globular cluster dynamics. In addition, extended monitoring may show that one or more of the pulsars are members of long-period binary systems.