A lower limit for the birth rate of pulsars

Abstract

Using experimental data on observed pulsars, we have estimated a lower limit for the birth rate of pulsars in our Galaxy to be B 1b = 0.0111 (plusminus0.0050) K pulsars yr-1 where K, the 'beam factor', allows for the possibility that only a fraction of all pulsars is beamed towards the Earth. If we take1 K to be 5, we obtain a mean birth rate of 1 pulsar per 18 yr while we can place a firmer lower bound with 95% confidence of 1 per 50 yr. Two important new features of the present approach are: (1) we do not assume any model for pulsars; (2) we have allowed for selection effects (in a model independent way). Apart from obtaining a more reliable number for the birth rate of pulsars, we conclude that the quantity P/(2P dot), where P is the period of the pulsar and P dot is its time derivative, is probably a good measure of age in "young" pulsars up to half a million years old, and that selection effects which have been neglected in all earlier calculations are significant. The present calculation reduces the discrepancy between pulsar and supernova birth rates.