Delensing Gravitational Wave Standard Sirens with Shear and Flexion Maps

TL;DR

This paper demonstrates that combining shear and flexion maps from advanced telescopes can significantly improve the accuracy of gravitational wave standard siren distance measurements by reducing lensing-induced uncertainties.

Contribution

It introduces a novel delensing method using combined shear and flexion maps to enhance SMBHB distance accuracy in gravitational wave cosmology.

Findings

Delensing with shear and flexion reduces distance errors by 30-40%.

Adding wide shear maps from space telescopes further reduces errors by 50%.

Improved delensing enhances SMBHBs' utility as independent cosmological probes.

Abstract

Supermassive black hole binary systems (SMBHB) are standard sirens -- the gravitational wave analogue of standard candles -- and if discovered by gravitational wave detectors, they could be used as precise distance indicators. Unfortunately, gravitational lensing will randomly magnify SMBHB signals, seriously degrading any distance measurements. Using a weak lensing map of the SMBHB line of sight, we can estimate its magnification and thereby remove some uncertainty in its distance, a procedure we call "delensing." We find that delensing is significantly improved when galaxy shears are combined with flexion measurements, which reduce small-scale noise in reconstructed magnification maps. Under a Gaussian approximation, we estimate that delensing with a 2D mosaic image from an Extremely Large Telescope (ELT) could reduce distance errors by about 30-40% for a SMBHB at z=2. Including an additional wide shear map from a space survey telescope could reduce distance errors by 50%. Such improvement would make SMBHBs considerably more valuable as cosmological distance probes or as a fully independent check on existing probes.