Credit:www.atnf.csiro.au

Revisiting GW170817 at milliarcsecond scale: high-precision constraints on jet geometry and Hubble’s constant
 

The historic detection of gravitational waves from the electromagnetically bright binary neutron star merger GW170817 enabled the first standard siren measurement of Hubble’s constant (H0). The accuracy and precision of this measurement depends crucially on how well the merger inclination angle is constrained, given its strong covariance with luminosity distance. Modeling the light curve of the jet’s afterglow provides constraints on inclination, but is highly dependent on the similarly uncertain jet opening angle. Past studies have improved on this by invoking high-resolution radio observations, obtained through very long baseline interferometry, to constrain the viewing angle. In this talk, I will present our Bayesian visibility-plane model-fitting framework that provides a more informed and robust measurement of the viewing geometry of GW170817, by including all relevant data, robustly handling systematic uncertainties, rigorously sampling model parameter space and using new hydrodynamical jet models. We extend our framework to fit for H0 directly, and consider various plausible peculiar velocity corrections to present a new and improved standard siren measurement of H0. Strikingly, we find our result to be in better agreement with one of the two precise and independent H0 measurements that are famously in tension.