The Local Low-Mass Binary Pulsar Population

Abstract

Using a fully self-consistent approach to account for known survey selection effects, we constrain the number and scale height of low-mass binary pulsars (LMBPs) in the local solar neighbourhood. Our results show that the local surface density of LMBPs with luminosities above 2.5 mJy kpc2 is ∼20 kpc−2. Assuming that these are long-lived (≲1010 yr) objects, their local birth rate is at least 2 10−9 kpc−2 yr−1. Whilst this is in excellent agreement with the birth rate of their proposed progenitors, the low-mass X-ray binaries, there are several uncertainties involved which could significantly increase our derived birth rate, perhaps by an order of magnitude. Models in which the scale height of LMBPs above the galactic plane exceeds 500 pc are found to be most consistent with the data. The mean space velocity at birth required to produce scale heights of this order in 1010 yr is found to be ≳ 80 km s−1.