Non-parametric inference of the neutron star equation of state from gravitational wave observations

Philippe Landry; Reed Essick

doi:10.1103/PhysRevD.99.084049

paper

Non-parametric inference of the neutron star equation of state from gravitational wave observations

arXiv:1811.12529 · doi:10.1103/PhysRevD.99.084049

Abstract

We develop a non-parametric method for inferring the universal neutron star (NS) equation of state (EOS) from gravitational wave (GW) observations. Many different possible realizations of the EOS are generated with a Gaussian process conditioned on a set of nuclear-theoretic models. These synthetic EOSs are causal and thermodynamically stable by construction, span a broad region of the pressure-density plane, and can be selected to satisfy astrophysical constraints on the NS mass. Associating every synthetic EOS with a pair of component masses $M_{1, 2}$ and calculating the corresponding tidal deformabilities $Λ_{1, 2}$ , we perform Monte Carlo integration over the GW likelihood for $M_{1, 2}$ and $Λ_{1, 2}$ to directly infer a posterior process for the NS EOS. We first demonstrate that the method can accurately recover an injected GW signal, and subsequently use it to analyze data from GW170817, finding a canonical deformability of $Λ_{1.4} = 16 0_{- 113}^{+ 448}$ and $p (2 ρ_{nuc}) = 1.3 5_{- 1.2}^{+ 1.8} \times 1 0^{34} dyn / cm^{2}$ for the pressure at twice the nuclear saturation density at 90 $%$ confidence, in agreement with previous studies, when assuming a loose EOS prior. With a prior more tightly constrained to resemble the theoretical EOS models, we recover $Λ_{1.4} = 55 6_{- 172}^{+ 163}$ and $p (2 ρ_{nuc}) = 4.7 3_{- 2.5}^{+ 1.4} \times 1 0^{34} dyn / cm^{2}$ . We further infer the maximum NS mass supported by the EOS to be $M_{max} = 2.0 9_{- 0.16}^{+ 0.37}$ ( $2.0 4_{- 0.002}^{+ 0.22}$ ) $M_{⊙}$ with the loose (tight) prior. The Bayes factor between the two priors is $B_{I}^{A} ≃ 1.12$ , implying that neither is strongly preferred by the data and suggesting that constraints on the EOS from GW170817 alone may be relatively prior-dominated.

27 pages, 12 figures; references added

Non-parametric inference of the neutron star equation of state from gravitational wave observations

Abstract

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