2009ApJ...693L.109K

We calculate the joint period-spin-down (P-) distributions of millisecond radio pulsars (MSRPs) for the standard evolutionary model in order to test whether the observed MSRPs are the unequivocal descendants of millisecond X-ray pulsars (MSXPs). The P- densities implied by the standard evolutionary model compared with observations suggest that there is a statistically significant overabundance of young/high magnetic field MSRPs. Taking biases due to observational selection effects into account, it is unlikely that MSRPs have evolved from a single coherent progenitor population that loses energy via magnetic dipole radiation after the onset of radio emission. By producing the P- probability map, we show with more than 95% confidence that the fastest spinning millisecond pulsars with high magnetic fields, e.g., PSR B1937+21, cannot be produced by the observed MSXPs within the framework of the standard model.