ar X iv : a st ro - p h / 04 11 16 0 v 2 9 N ov 2 00 4 The Millisecond Pulsars in NGC 6760

We present the results of recent Arecibo and Green Bank observations of the globular cluster NGC 6760. Using Arecibo, a phase-coherent timing solution has been obtained for the previously known binary pulsar in this cluster, PSR J1911+0102A. We have also discovered a new millisecond pulsar in NGC 6760, PSR J1911+0101B, an isolated object with a rotational period of 5.38ms and a dispersion measure DM = 196.7 cm pc. Both pulsars are located within 1.3 core radii of the cluster center and have negative period derivatives. The resulting lower limits for the accelerations of the pulsars are within the range expected given a simple model of the cluster. A search for eclipses in the PSR J1911+0102A binary system using both telescopes yielded negative results. The corresponding limits on the extra gas column density at superior conjunction are consistent with the hypothesis that the observational properties of ultra-low-mass binary pulsars like PSR J1911+0102A are strongly affected by the inclination of the orbital plane of the system. Among globular cluster pulsar populations, that of NGC 6760 exhibits one of the largest known spreads in DM. This quantity seems to be roughly proportional to a cluster’s central DM; this suggests that the observed spread is caused by a turbulent interstellar medium at spatial scales of 1 pc. NAIC, Arecibo Observatory, HC3 Box 53995, PR 00612, USA; [email protected] Department of Physics, Rutherford Physics Building, McGill University, 3600 University Street, Montreal, Quebec, H3A 2T8, Canada; [email protected] Physics Department, Princeton University, Box 708, Princeton, NJ 08544; [email protected] National Radio Astronomy Observatory, 520 Edgemont Rd., Charlottesville, VA 22903 USA; [email protected] University of Manchester, Jodrell Bank Observatory, Macclesfield, Cheshire, SK11 9DL, UK; [email protected] Department of Physics and Astronomy University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 Canada; [email protected]