Discovery of four binary millisecond pulsars

We present detailed parameters for four binary millisecond pulsars discovered during a survey of the southern sky with the Parkes radio telescope. Subsequent observations using the Parkes and Jodrell Bank radio telescopes have determined that the pulsars, PSRs J1603-7202, J1804-2717, 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 Jodrell 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 known spin periods, should match the true spin period distribution more closely than the observed one. For periods greater than or similar to 3 ms, the distribution is well constrained by this method. At shorter periods, however, the distribution is highly uncertain because of small-number statistics.