Constraints on the neutron star equation of state from AT2017gfo using radiative transfer simulations

TL;DR

This paper models the electromagnetic counterpart of GW170817 using advanced radiative transfer simulations to derive constraints on neutron star properties and the equation of state by combining gravitational wave and electromagnetic data.

Contribution

It introduces wavelength-dependent opacities and emissivities from atomic data into kilonova modeling, enabling more realistic simulations and tighter constraints on neutron star parameters.

Findings

Upper bound on mass ratio q ≤ 1.38

Lower bound on tidal deformability Λ ≥ 197

Rules out soft equations of state

Abstract

The detection of the binary neutron star GW170817 together with the observation of electromagnetic counterparts across the entire spectrum inaugurated a new era of multi-messenger astronomy. In this study we incorporate wavelength-dependent opacities and emissivities calculated from atomic-structure data enabling us to model both the measured lightcurves and spectra of the electromagnetic transient AT2017gfo. Best-fits of the observational data are obtained by Gaussian Process Regression, which allows us to present posterior samples for the kilonova and source properties connected to GW170817. Incorporating constraints obtained from the gravitational wave signal obtained by the LIGO-Virgo Scientific Collaboration, we present a $90\%$ upper bound on the mass ratio $q \lesssim 1.38$ and a lower bound on the tidal deformability of $\tilde{\Lambda} \gtrsim 197$, which rules out sufficiently soft equations of state. Our analysis is a path-finder for more realistic kilonova models and shows how the combination of gravitational wave and electromagnetic measurements allow for stringent constraints on the source parameters and the supranuclear equation of state.