Four new millisecond pulsars in the galactic disk

Abstract

We report the discovery of fourmillisecond pulsars as part of a conntinuing survey of the SouthernHemisphere with the Parkes radio telescope. Three of the pulsars, PSRsJ0613-0200, J1455-3330, and J1643-1224, are in circular orbits withlow-mass (approximately 0.1-0.3 solar mass) companions. The fourthpulsar, PSR J1730-2304, has a period of 8.12 ms and appears to besolitary. Based on the results of the Parkes and other surveys, weestimate the number of low-mass binary pulsars with luminositiesgreater than 2.5 mJy/sq kpc in the Galactic disk to be at least 40,000.If the lifetimes of these systems are comparable to the age of thedisk then, as a group, their birthrate is consistent with that oftheir proposed progenitors, the low-mass X-ray binaries. The binarypulsars give some support to the relation between orbital period andcompanion mass discussed by Joss, Rappaport, & Lewis and the relationbetween orbital eccentricity and orbital period discussed by Phiney.These results are consistent with the idea that the neutron starshave been spun up by accreting matter form their companion stars.