Abstract
ABSTRACT We present a rapid analytic framework for predicting kilonova light curves following neutron star (NS) mergers, where the main input parameters are binary-based properties measurable by gravitational wave detectors (chirp mass and mass ratio, orbital inclination) and properties dependent on the nuclear equation of state (tidal deformability, maximum NS mass). This enables synthesis of a kilonova sample for any NS source population, or determination of the observing depth needed to detect a live kilonova given gravitational wave source parameters in low latency. We validate this code, implemented in the public mosfit package, by fitting it to GW170817. A Bayes factor analysis overwhelmingly (B > 1010) favours the inclusion of an additional luminosity source in addition to lanthanide-poor dynamical ejecta during the first day. This is well fit by a shock-heated cocoon model, though differences in the ejecta structure, opacity or nuclear heating rate cannot be ruled out as alternatives. The emission thereafter is dominated by a lanthanide-rich viscous wind. We find the mass ratio of the binary is q = 0.92 ± 0.07 (90 per cent credible interval). We place tight constraints on the maximum stable NS mass, MTOV $=2.17^{+0.08}_{-0.11}$ M⊙. For a uniform prior in tidal deformability, the radius of a 1.4-M⊙ NS is R1.4 ∼ 10.7 km. Re-weighting with a prior based on equations of state that support our credible range in MTOV, we derive a final measurement R1.4 $=11.06^{+1.01}_{-0.98}$ km. Applying our code to the second gravitationally detected NS merger, GW190425, we estimate that an associated kilonova would have been fainter (by ∼0.7 mag at 1 d post-merger) and declined faster than GW170817, underlining the importance of tuning follow-up strategies individually for each GW-detected NS merger.
Highlights
The first binary neutron star (NS) merger detected through its gravitational wave emission, GW170817 (Abbott et al 2017a), was accompanied by both a short gamma-ray burst (GRB; Goldstein et al 2017; Savchenko et al 2017) and an optical counterpart (Arcavi et al 2017; Coulter et al 2017; Lipunov et al 2017; Soares-Santos et al 2017; Tanvir et al 2017; Valenti et al 2017)
We present a rapid analytic framework for predicting kilonova light curves following neutron star (NS) mergers, where the main input parameters are binary-based properties measurable by gravitational wave detectors and properties dependent on the nuclear equation of state
We provide a fast, analytic forward model for kilonova light curves that is completely specified by the binary configuration and equation of state (EoS)-dependent properties
Summary
Cowperthwaite et al 2017; Dıaz et al 2017; Drout et al 2017; Evans et al 2017; Hu et al 2017; Kasliwal et al 2017; McCully et al 2017; Pian et al 2017; Shappee et al 2017; Smartt et al 2017; Tanvir et al 2017; Troja et al 2017; Utsumi et al 2017; Valenti et al 2017; Nicholl et al 2017a; Pozanenko et al 2018). We provide a fast, analytic forward model for kilonova light curves that is completely specified by the binary configuration and EoS-dependent properties Fitting such a model to observed kilonova data allows one to measure fundamental premerger properties even in the absence of a GW signal, or to use GW information when available as priors for multimessenger inference. By fitting the rich observed data set, we will show the power of using GW results as priors, constrain the physical origins of the different emission components, and present new measurements of the mass ratio of the progenitor system, the viewing angle, and the EoS-dependent quantities R1.4 and MTOV. A set of kilonova model light curves produced using our code is available for download (see the Data Availability section)
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