New limits on the population of normal and millisecond pulsars in the Large and Small Magellanic Clouds

TL;DR

This paper estimates the total populations and birth rates of normal and millisecond pulsars in the Large and Small Magellanic Clouds, revealing a large hidden pulsar population and setting upper limits on MSP numbers.

Contribution

It provides the first detailed population estimates and birth rate calculations for pulsars in the Magellanic Clouds, incorporating detection thresholds and beaming effects.

Findings

Estimated 17,900 and 10,900 normal pulsars in LMC and SMC.

Pulsar birth rates are 0.5-1 per century, consistent with supernova observations.

Upper limits of 15,000 and 23,000 for MSPs in LMC and SMC.

Abstract

We model the potentially observable populations of normal and millisecond radio pulsars in the Large and Small Magellanic Clouds (LMC and SMC) where the known population currently stands at 19 normal radio pulsars. Taking into account the detection thresholds of previous surveys, and assuming optimal period and luminosity distributions based on studies of Galactic pulsars, we estimate there are (1.79 +/- 0.20) x 10^4 and (1.09 +/- 0.16) x 10^4 normal pulsars in the LMC and SMC respectively. When we attempt to correct for beaming effects, and the fraction of high-velocity pulsars which escape the clouds, we estimate birth rates in both the LMC and SMC to be comparable and in the range 0.5--1 pulsar per century. Although higher than estimates for the rate of core-collapse supernovae in the clouds, these pulsar birth rates are consistent with historical supernova observations in the past 300 yr. A substantial population of active radio pulsars (of order a few hundred thousand) have escaped the LMC and SMC and populate the local intergalactic medium. For the millisecond pulsar (MSP) population, the lack of any detections from current surveys leads to respective upper limits (at the 95% confidence level) of 15,000 for the LMC and 23,000 for the SMC. Several MSPs could be detected by a currently ongoing survey of the SMC with improved time and frequency resolution using the Parkes multibeam system. Giant-pulse emitting neutron stars could also be seen by this survey.