Delensing Gravitational Wave Standard Sirens with Shear and Flexion Maps

Understand

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.