Prospects for detecting neutron star–white dwarf mergers with decihertz gravitational-wave observatories

Abstract

ABSTRACT Based on different neutron star–white dwarf (NS–WD) population models, we investigate the prospects of gravitational-wave (GW) detections for NS–WD mergers, with the help of early warnings from two space-borne decihertz GW observatories, DO-Optimal and DECIGO. We not only give quick assessments of the GW detection rates for NS–WD mergers with the two decihertz GW detectors, but also report systematic analyses on the characteristics of GW-detectable merger events using the method of Fisher matrix. With a sufficient 1-d early-warning time, the yearly GW detection number for DO-Optimal is in the range of (1.5–1.9) × 103, while it is (3.3–4.6) × 104 for DECIGO. More importantly, our results show that most NS–WD mergers can be localized with an uncertainty of $\mathcal {O}(10^{-2})\, \mathrm{deg}^2$. Given the NS–WD merger as a possible origin for a peculiar long-duration gamma-ray burst, GRB 211211A, followed with kilonova-like emissions, we further suggest that the GW early-warning detection would allow future electromagnetic telescopes to get prepared to follow up transients after some special NS–WD mergers. Based on our analyses, we emphasize that such a feasible ‘wait-for’ pattern can help to firmly identify the origin of GRB 211211A-like events in the future and bring excellent opportunities for the multimessenger astronomy.