Constraining the luminosity function parameters and population size of radio pulsars in globular clusters

Studies of theGalactic population of radio pulsars have shown that their luminosity distribution appears to be log-normal in form. We investigate some of the consequences that occur when one applies this functional form to populations of pulsars in globular clusters. We use Bayesian methods to explore constraints on the mean and standard deviation of the luminosity function, as well as the total number of pulsars, given an observed sample of pulsars down to some limiting flux density, accounting for measurements of flux densities of individual pulsars as well as diffuse emission from the direction of the cluster. We apply our analysis to Terzan 5, 47 Tucanae and M28, and demonstrate, under reasonable assumptions, that the number of potentially observable pulsars should be within 95 per cent credible intervals of 147⁺¹¹²_-65, 83⁺⁵⁴_-35 and 100⁺⁹¹_-52, respectively. Beaming considerations would increase the true population size by approximately a factor of 2. Using non-informative priors, however, the constraints are not tight due to the paucity and quality of flux density measurements. Future cluster pulsar discoveries and improved flux density measurements would allow this method to be used to more accurately constrain the luminosity function, and to compare the luminosity function between different clusters.