Implications of PSR J0737-3039B for the Galactic NS-NS Binary Merger Rate

TL;DR

This paper refines the Galactic neutron star binary merger rate by correcting observational biases in the Double Pulsar system, leading to updated estimates of gravitational wave detection rates and implications for future observations.

Contribution

It provides a new estimate of the NS-NS merger rate by incorporating biases from both pulsars in the Double Pulsar system, challenging previous assumptions.

Findings

Galactic NS-NS merger rate estimated at 21_{-14}^{+28} per Myr.

Expected gravitational wave detection rate of 8^{+10}_{-5} per year.

Small beaming correction factor (~2) supports bipolar pulsar emission models.

Abstract

The Double Pulsar (PSR J0737-3039) is the only neutron star-neutron star (NS-NS) binary in which both NSs have been detectable as radio pulsars. The Double Pulsar has been assumed to dominate the Galactic NS-NS binary merger rate R_g among all known systems, solely based on the properties of the first-born, recycled pulsar (PSR J0737-3039A, or A) with an assumption for the beaming correction factor of 6. In this work, we carefully correct observational biases for the second-born, non-recycled pulsar (PSR J0737-0737B, or B) and estimate the contribution from the Double Pulsar on R_g using constraints available from both A and B. Observational constraints from the B pulsar favour a small beaming correction factor for A (~2), which is consistent with a bipolar model. Considering known NS-NS binaries with the best observational constraints, including both A and B, we obtain R_g=21_{-14}^{+28} per Myr at 95 per cent confidence from our reference model. We expect the detection rate of gravitational waves from NS-NS inspirals for the advanced ground-based gravitational-wave detectors is to be 8^{+10}_{-5} per yr at 95 per cent confidence. Within several years, gravitational-wave detections relevant to NS-NS inspirals will provide us useful information to improve pulsar population models.