The mass distribution of Galactic double neutron stars: constraints on the gravitational-wave sources like GW170817

Abstract

The merger event of double neutron star (DNS) system (GW170817) was detected by the gravitational-wave (GW) detectors (Advanced LIGO and Advanced Virgo) in 2017 for the first time, so their mass distribution has become a significant topic with the new round GW hunting (O3) in 2019. A few models (e.g. Gaussian, two-Gaussian, or mixture-Gaussian) were adopted to draw the mass distribution of observed Galactic DNS systems, however, there is no a confirmed model now due to the small size of DNS samples (N < 20). Here we focus on determining the most probable distribution ranges of DNS masses without model selection by assuming the neutron star masses to be uniformly distributed between the lower and upper bounds. We apply a Bayesian analysis and Markov chain Monte Carlo simulation to 15 Galactic DNS systems, and obtain that the component masses of DNS systems should mainly fall in the range of 1.165–1.590 M⊙, and the predominant ranges for the total mass, mass ratio, and chirp mass lie in 2.535–2.867 M⊙, 0.741–0.995, and 1.115–1.237 M⊙, respectively. Our results are in agreement with the properties of DNS in GW170817, whose 90 per cent credible intervals for the component masses, total masses, mass ratio, and chirp masses are 1.16–1.60 M⊙, $2.73_{-0.01}^{+0.04}\, \mathrm{ M}_\odot$, 0.73–1.00, and $1.186_{-0.001}^{+0.001}\, \mathrm{ M}_\odot$, respectively. The above similarity is an important indicator that reveals the source of GW170817 to be a DNS system from the galaxy NGC 4993, and our results can be tested by the forthcoming GW hunting O3.

The Gravitational Wave Universe Toolbox: A software package to simulate observation of the Gravitational Wave Universe with different detectors

“…The default parameters are the mean m = 1.4 M , the mass dispersion σ m = 0.5 M , upper cut m cut,low = 1.1 M , m cut,high = 2.5 M ; we apply also a Gaussian spin model, with a smaller dispersion σ χ = 0.05. These choices are roughly agree with observations (Valentim et al 2011;Özel et al 2012;Kiziltan et al 2013;Miller & Miller 2015;Farrow et al 2019;Zhang et al 2019)…”

An ASKAP Search for a Radio Counterpart to the First High-significance Neutron Star–Black Hole Merger LIGO/Virgo S190814bv

“…The event was classified as a neutron star-black hole (NSBH) merger, where the lighter component has a mass < 3 M , and the heavier component has a mass > 5 M , (LIGO Scientific Collaboration and Virgo Collaboration et al 2019b). The accuracy of this classification is dependent on the physical upper-limit for neutron star mass which is not well constrained, but may be less than the above definition (Zhang et al 2019;Cromartie et al 2019). The probability of there being matter outside the remnant object is < 1% (LIGO Scientific Collaboration and Virgo Collaboration et al 2019a), therefore the expected nature of any electromagnetic radiation from the merger (if any) is unclear.…”

Filling the Mass Gap: How Kilonova Observations Can Unveil the Nature of the Compact Object Merging with the Neutron Star

“…The BH mass distribution observed so far in coalescing binaries is broad (The LIGO Scientific Collaboration et al 2018), extending up to 50 +16.6 −10.2 M , with the lightest BH carrying a mass 7.6 +1.3 −2.1 M , close to the mean BH mass in observed Galactic X-ray binaries of ∼ 7.8 ± 1.2 M ( Özel et al 2010). Double NS systems observed so far carry masses in the interval 1.165 M − 1.590 M (Zhang et al 2019), and the NS with the highest and best estimated mass is the radio pulsar J0740+6620 with M NS = 2.14 +0.10 −0.09 M in a lowmass binary (Cromartie et al 2019). Thus, observations appear to indicate a discontinuity between the observed mass distributions of NSs and stellar BHs, called mass gap", located approximately between ≈ 3 M (the maximum NS mass inferred from causality arguments) and ∼ 5 M (Lattimer & Prakash 2001).…”

“…The unbound NS material ("ejecta") is thought to produce kilonova emission (Lattimer & Schramm 1974;Li & Paczyński 1998;Metzger 2017). Moreover, Shapiro (2017); Paschalidis (2017); Ruiz et al (2018) showed that after a BHNS merger a relativistic jet can be launched, powering a short gamma-ray burst (sGRB) (Eichler et al 1989;Narayan et al 1992) and GRB afterglow emission (Sari et al 1998;D'Avanzo et al 2018;Ghirlanda et al 2018;Salafia et al 2019 (Zhang et al 2019), and the NS with the highest and best estimated mass is the radio pulsar J0740+6620 with M NS = 2.14 +0.10 −0.09 M in a lowmass binary (Cromartie et al 2019). Thus, observations appear to indicate a discontinuity between the observed mass distributions of NSs and stellar BHs, called mass gap", located approximately between ≈ 3 M (the maximum NS mass inferred from causality arguments) and ∼ 5 M (Lattimer & Prakash 2001).…”