Galactic distribution and evolution of pulsars

Abstract

The distribution of pulsars with respect to period, z-distance, luminosity, and galactocentric radius has been investigated using data from three extensive pulsar surveys. It is shown that selection effects only slightly modify the observed period and z-distributions but strongly affect the observed luminosity function and galactic distribution. These latter two distributions are computed from the Jodrell Bank and Arecibo data, using an iterative procedure. The largest uncertainties in our results are the result of uncertainty in the adopted distance scale. Therefore, where relevant, separate calculations have been made for two values of the average interstellar electron density, , 0.02 cm/sup -3/ and 0.03 cm/sup -3/.The derived luminosity function is closely represented by a power law with index (for logarithmic luminosity intervals) close to -1. For =0.03 cm/sup -3/, the density of potentially observable pulsars is about 90 kpc/sup -2/ in the local region and increases with decreasing galactocentric radius. These distributions imply that the total number of pulsars in the Galaxy is about 10/sup 5/. If only a fraction of all pulsars are observable because of beaming effects, then the total number in the Galaxy is correspondingly greater.Recent observations of pulsar proper motions show that pulsars are generally high-velocity objects.more » The observed z-distribution of pulsars implies that the mean age of observable pulsars does not exceed 2 x 10/sup 6/ years. With this mean age the pulsar birthrate required to maintain the observed galactic distribution is 10/sup -4/ yr/sup -1/ kpc/sup -2/ in the local region and one pulsar birth every 6 years in the Galaxy as a whole. For =0.02 cm/sup -3/, the corresponding rate is one birth every 40 years. These rates exceed most estimates of supernova occurrence rates and may require that all stars with mass greater than approx.2.5 Msun form pulsars at the end of their evolutionary life.« less