Inference of Neutron Star Mass Distributions and the Dense Matter Equation of State from Multimessenger Observations

Abstract We construct a combined model to incorporate neutron star (NS) mass measurements with electromagnetic mass–radius constraints and gravitational-wave observations using Bayesian inference. We use different mass distributions for three populations depending on the companion stars: double neutron star binaries, NS–white dwarf binaries, and low-mass X-ray binaries (LMXBs). To observe the effects of different parameterizations, we use two equation-of-state (EoS) models: a piecewise polytrope and a fixed-sound-speed model at high densities, in combination with a low-density EoS. Our results show that the mass distributions of these NS populations are distinct and sensitive to the EoS prior choices. In addition, we show for the first time that using a uniform prior on the observable NS maximum mass, rather than a nuisance parameter in the unknown high-density EoS, shifts the posterior maximum mass to larger values. For polytropic EoSs, the maximum mass posterior changes from M max = 2.0 9 − 0.07 + 0.18 M ⊙ to 2.1 5 − 0.10 + 0.19 M ⊙ at a 90% confidence level. This change in prior also impacts the shape of the mass distribution for NSs in LMXBs, shifting the posterior for the population mean from μ lmxb = 1.5 1 − 0.13 + 0.13 M ⊙ to 1.6 2 − 0.12 + 0.15 M ⊙ at a 68% confidence level.