Neutron Star Population Dynamics. I. Millisecond Pulsars

We study the field millisecond pulsar (MSP) population to infer its intrinsicdistribution in spin period and luminosity and to determine its spatialdistribution within the Galaxy. Our likelihood analysis on data from extantsurveys (22 pulsars with periods <20 ms) accounts for important selectioneffects. We infer a minimum period cutoff P(min) > 0.65 ms (99% confidence), aperiod distribution proportional to P^{-2.0 +- 0.33} and a pseudo-luminositydistribution proportional to L_p^{-2.0 +- 0.2} (where L_p = flux density timesdistance^2, for L_p >= 1.1 mJy kpc^2). We find a vertical scale height0.65{+0.16,-0.12} kpc. We use our results to estimate the total number andbirthrate of MSPs in the disk of the Galaxy. We limit the density contributionof a diffuse halo-like component to <1% of the midplane value. The MSP velocitydispersion is smaller that that of young, long-period pulsars by about a factorof 5. Our best estimate of the 1D velocity kick that is unique to MSP evolutionis approximately 40 km s^-1. We discuss the evolutionary relationship of MSPsand low-mass X-ray binaries and prospects for future searches for MSPs.Comment: 53 pages, 12 Postscript figures, LaTeX/AASTeX (aasp4), to appear Ap. J. 482, 1997 June 2