DISCOVERY OF 4 BINARY MILLISECOND PULSARS

We present detailed parameters for four binary millisecond pulsars dis covered during a survey of the southern sky with the Parkes radio tele scope. Subsequent observations using the Parkes and Jodrell Bank radio telescopes have determined that the pulsars, PSRs J1603-7202, J1804-2 717, J1911-1114 and J2129-5721, have spin periods ranging between 3.6 and 14.8 ms and are in circular orbits of periods between 2.7 and 11.1 d with low-mass (similar to 0.1-0.3 Mo) companions. The Parkes survey is now complete and has discovered a total of 17 millisecond pulsars; combining these results with large-area surveys at Arecibo and Jodrel l Bank, the total number of millisecond pulsars known in the Galactic disc (i.e. not inside globular clusters) is 35. Based on this sample, we use a self-consistent Monte Carlo approach to derive the corrected pulsar spin period distribution which, over the range of presently kno wn spin periods, should match the true spin period distribution more c losely than the observed one. For periods greater than or similar to 3 ms, the distribution is well constrained by this method. At shorter p eriods, however, the distribution is highly uncertain because of small -number statistics.