The Challenges Ahead for Multimessenger Analyses of Gravitational Waves and Kilonova: a Case Study on GW190425

Abstract

In recent years, there have been significant advances in multi-messenger astronomy due to the discovery of the first, and so far only confirmed, gravitational wave event with a simultaneous electromagnetic (EM) counterpart, as well as improvements in numerical simulations, gravitational wave (GW) detectors, and transient astronomy. This has led to the exciting possibility of performing joint analyses of the GW and EM data, providing additional constraints on fundamental properties of the binary progenitor and merger remnant. Here, we present a new Bayesian framework that allows inference of these properties, while taking into account the systematic modeling uncertainties that arise when mapping from GW binary progenitor properties to photometric light curves. We extend the relative binning method presented in Zackay et al. ( 2018) to include extrinsic GW parameters for fast analysis of the GW signal. The focus of our EM framework is on light curves arising from r-process nucleosynthesis in the ejected material during and after merger, the so called kilonova, and particularly on black hole -neutron star systems. As a case study, we examine the recent detection of GW190425, where the primary object is consistent with being either a black hole (BH) or a neutron star (NS). We show quantitatively how improved mapping between binary progenitor and outflow properties, and/or an increase in EM data quantity and quality are required in order to break degeneracies in the fundamental source parameters.

GWTC-3: Compact Binary Coalescences Observed by LIGO and Virgo During the Second Part of the Third Observing Run

“…It has been suggested that due to their faintness and fast evolution, searches by optical surveys for kilonovae within a distance up to 200 Mpc require early observations down to magnitude 21 [554]. Future counterpart detections as soon as the next observing run are likely to place strong, multimessenger constraints on the equation of state of NSs, and the Hubble constant [555][556][557][558][559].…”

Constraints on the dense matter equation of state and neutron star properties from NICER's mass-radius estimate of PSR J0740+6620 and multimessenger observations

“…Here we analyze the bolometric luminosity of GW170817 (as compiled in Kasliwal et al 2017) via the new Bayesian framework outlined in Raaijmakers et al (2021b). We consider a two-component kilonova model, where the first component, the dynamical ejecta, is associated with material ejected through tidal forces and the shock interface between the two neutron stars (see, e.g., Radice et al 2018, and references therein).…”

Estimating outflow masses and velocities in merger simulations: impact of r-process heating and neutrino cooling

“…Nevertheless, uncertainties in the numerical simulations used to model these outflows, in the properties of the elements produced during the r-process, and in the heating rate of the ejecta due to radioactive decays create significant difficulties when attempting to interpret kilonovae signals, with highly uncertain error bars in any inference made about the parameters of the merging compact objects (see e.g. [40][41][42]).…”

“…Predicting the properties of matter outflows in NSNS and BHNS mergers is crucial to our ability to perform detailed analysis of kilonovae. Such predictions are typically made by developing analytical fits to the results of merger and post-merger simulations of these systems [42][43][44][45][46][47]. A reliable determination of the properties of unbound material in merger simulations is accordingly important to kilonova modeling efforts.…”