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 multimessenger 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. 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 or a neutron star. 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.

Long-term 3D-MHD Simulations of Black Hole Accretion Disks formed in Neutron Star Mergers

“…The extrapolated outflow for our 3D MHD model bhns predicts 6 − 8% of the initial torus mass, which is consistent with the previously-found enhancement in mass ejection by MHD relative to viscous hydrodynamics at smaller compactnesses when evolving both to ∼ 10 s (Fernández et al 2019a). Our results inform analytic fits to fractions of the initial disk mass ejected like that of Raaijmakers et al (2021), which has the enhancement in mass ejection due to magnetic effects relative to viscous hydrodynamics as a free parameter. More 3D MHD simulations at different compactness and with various initial magnetic field geometries are needed to improve the predictive power of these fits.…”

“…The lack of counterparts can be explained by either observational factors (e.g., Foley et al 2020), smaller amounts of mass ejected than in GW170817 given different possible binary properties, or a combination of the two. Better understanding the physics of mass ejection is therefore of key importance to improve predictions and understanding of future detections (e.g., Raaijmakers et al 2021).…”

A Channel to Form Fast-spinning Black Hole–Neutron Star Binary Mergers as Multimessenger Sources

“…However, despite many efforts toward the follow-up observations, no confirmed EM counterpart candidate was identified (e.g., Coughlin et al 2020aCoughlin et al , 2020bGompertz et al 2020b;Kasliwal et al 2020;Page et al 2020;Anand et al 2021;Becerra et al 2021). The tidal disruption probability of NSBH mergers and the brightness of EM signals depend on NS mass, NS equation of state (EOS), BH mass, and especially BH projected aligned spin (e.g., Kyutoku et al 2015;Kawaguchi et al 2016;Foucart et al 2018;Barbieri et al 2019;Zhu et al 2020Zhu et al , 2021aZhu et al , 2021bZhu et al , 2021cRaaijmakers et al 2021). Disrupted events associated with brighter EM signals tend to occur only if an NSBH binary has a low-mass NS component with a stiff EOS and a low-mass BH component with a high projected aligned spin.…”

Inferring kilonova population properties with a hierarchical Bayesian framework I : Non-detection methodology and single-event analyses

“…It will also help in understanding the relationship and breaking the degeneracy that exists between binary parameters (equation of state, spin and mass ratio) (Foucart et al 2018;Hinderer et al 2019;Radice & Dai 2019;Zhu et al 2020), ejecta mass and KN light curve morphology. (Coughlin et al 2019a;Hotokezaka & Nakar 2020;Breschi et al 2021;Raaijmakers et al 2021). The future GW and EM multi-messenger landscape will provide the opportunity to explore this further.…”

“…Observations were recorded in the ultraviolet, optical and near-infrared (Andreoni et al 2017;Chornock et al 2017;Coulter et al 2017;Cowperthwaite et al 2017;Drout et al 2017;Evans et al 2017;Kasliwal et al 2017Kasliwal et al , 2019aKilpatrick et al 2017;Lipunov et al 2017;McCully et al 2017;Nicholl et al 2017;Shappee et al 2017;Soares-Santos et al 2017;Pian et al 2017;Smartt et al 2017;Tanvir et al 2017;Utsumi et al 2017). These observations have highlighted the ability to test models of KNe and provide constraints on the ejecta mass and velocity Cowperthwaite et al 2017;Perego et al 2017;Pian et al 2017;Smartt et al 2017;Tanaka et al 2017;Waxman et al 2018;Coughlin et al 2019a;Kawaguchi et al 2020;Heinzel et al 2021;Raaijmakers et al 2021), r-process elemental abundances (Côté et al 2018;Hotokezaka et al 2018;Radice et al 2018;Tanaka et al 2018;Hotokezaka & Nakar 2020;Siegel 2019), the NS equation of state (Foucart et al 2018;Coughlin et al 2018a;Radice & Dai 2019;Hinderer et al 2019;…”