How can LISA probe a population of GW190425-like binary neutron stars in the Milky Way?

Valeriya Korol,Mohammadtaher Safarzadeh

doi:10.1093/mnras/stab310

Abstract

ABSTRACT The nature of GW190425, a presumed binary neutron star (BNS) merger detected by the LIGO/Virgo Scientific Collaboration (LVC) with a total mass of $3.4^{+0.3}_{-0.1}$ M⊙, remains a mystery. With such a large total mass, GW190425 stands at five standard deviations away from the total mass distribution of Galactic BNSs of 2.66 ± 0.12 M⊙. LVC suggested that this system could be a BNS formed from a fast-merging channel rendering its non-detection at radio wavelengths due to selection effects. BNSs with orbital periods less than a few hours – progenitors of LIGO/Virgo mergers – are prime target candidates for the future Laser Interferometer Space Antenna (LISA). If GW190425-like binaries exist in the Milky Way, LISA will detect them within the volume of our Galaxy and will measure their chirp masses to better than 10 per cent for those binaries with gravitational wave frequencies larger than 2 mHz. This work explores how we can probe a population of Galactic GW190425-like BNSs with LISA and investigate their origin. We assume that the Milky Way’s BNS population consists of two distinct subpopulations: a fraction w1 that follows the observed Galactic BNS chirp mass distribution and w2 that resembles chirp mass of GW190425. We show that LISA’s accuracy on recovering the fraction of GW190425-like binaries depends on the BNS merger rate. For the merger rates reported in the literature, $21{-}212\,$ Myr−1, the error on the recovered fractions varies between ∼30 and 5 per cent.

Highlights

GW190425 is a compact object merger with a total mass of 3.4+−00..31 M, that was recently detected by the LIGO/Virgo Collaboration (LVC, Abbott et al 2020)
We start by assuming the fraction of binary neutron star (BNS) that resemble GW190425 to be w2 = 0.2 and we set the Galactic merger rate to be 140 Myr−1, which corresponds to 33 BNSs with frequencies higher than 2 mHz in the Galaxy
We have investigated whether future observations of Galactic BNS with Laser Interferometer Space Antenna (LISA) and LISA’s chirp mass measurement can elucidate on the nature of heavy BNS like GW190425

Summary

Introduction

GW190425 is a compact object merger with a total mass of 3.4+−00..31 M , that was recently detected by the LIGO/Virgo Collaboration (LVC, Abbott et al 2020). GW190425 is a compact object merger with a total mass of 3.4+−00..31. If GW190425 is a binary neutron star (BNS) merger, its total mass is inconsistent with the observed Galactic BNS population that shows a narrow range in the total mass of ≈ 2.66 ± 0.12 M (Farrow et al 2019). LVC suggests that GW190425 might belong to a class of BNSs born from a fastmerging channel. In this hypothesis, massive BNSs like GW190425 merge on timescales of 10 - 100 Myr due to being formed with short orbital periods through unstable case-BB mass transfer or with high eccentricities through large natal kicks (e.g. Tauris et al 2017; Romero-Shaw et al 2020; Galaudage et al 2020). Short life-times and severe Doppler smearing, which affects short-period systems, make these binaries invisible to radio telescopes and hard to find in our Galaxy (Cameron et al 2018; Pol et al 2020)

Methods

Results

Conclusion