Four new millisecond pulsars in the Galactic disk
D. R. Lorimer (The University of Manchester, NRAL, Jodrell Bank, UK),
L. Nicastro (The University of Manchester, NRAL, Jodrell Bank, UK),
A. G. Lyne (The University of Manchester, NRAL, Jodrell Bank, UK),
M. Bailes (ATNF, CSIRO, Australia),
R. N. Manchester (ATNF, CSIRO, Australia),
S. Johnston (ATNF, CSIRO, Australia),
J. F. Bell (MSSSO, Australian National University, Australia),
N. D'Amico (Istituto di Radioastronomia del CNR, Bologna, Italy),
P. A. Harrison (The University of Manchester, NRAL, Jodrell Bank, UK)
Abstract We report the discovery of four millisecond pulsars as part of a continuing survey of the Southern Hemisphere with the Parkes radio telescope. Three of the pulsars, PSRs J0613-0200, J1455-3330 and J1643-1224 are in circular orbits with low-mass (~0.1-0.3 Msun) companions. The fourth pulsar, PSR J1730-2304 has a period of 8.12 ms and appears to be solitary. Based on the results of the Parkes and other surveys, we estimate the number of low-mass binary pulsars with luminosities greater than 2.5 mJy kpc^2 in the Galactic disk to be at least 40,000. If the lifetimes of these systems are comparable to the age of the disk then, as a group, their birth-rate is consistent with that of their proposed progenitors, the low-mass X-ray binaries. The binary pulsars give some support to the relation between orbital period and companion mass discussed by Joss, Rappaport & Lewis (1987) and the relation between orbital eccentricity and orbital period discussed by Phinney (1992). These results are consistent with the idea that the neutron stars have been spun up by accreting matter from their companion stars.
Key words: pulsars: individual (PSR J0613-0200, PSR J1455-3330, PSR J1643-1224, PSR J1730-2304)