Observations of 20 Millisecond Pulsars in 47 Tucanae at 20 Centimeters

We have used a new observing system on the Parkes radio telescope to carryout a series of pulsar observations of the globular cluster 47 Tucanae at 20-cmwavelength. We detected all 11 previously known pulsars, and have discoverednine others, all of which are millisecond pulsars in binary systems. We havesearched the data for relatively short orbital period systems, and found onepulsar with an orbital period of 96 min, the shortest of any known radiopulsar. The increased rate of detections with the new system resulted in improvedestimates of the flux density of the previously known pulsars, determination ofthe orbital parameters of one of them, and a coherent timing solution foranother one. Five of the pulsars now known in 47 Tucanae have orbital periodsof a few hours and implied companion masses of only ~ 0.03 Msun. Two of theseare eclipsed at some orbital phases, while three are seen at all phases at 20cm but not always at lower frequencies. Four and possibly six of the otherbinary systems have longer orbital periods and companion masses ~ 0.2 Msun,with at least two of them having relatively large orbital eccentricities. All20 pulsars have rotation periods in the range 2-8 ms.Comment: 15 pages, 6 embedded EPS figures, to be published in The Astrophysical Journa