Mitigating the counterpart selection effect for standard sirens

TL;DR

This paper introduces a new formalism to mitigate the systematic bias caused by electromagnetic counterpart selection effects in standard siren measurements of the Hubble constant, aiming to improve accuracy.

Contribution

The authors develop a novel formalism that reduces systematic uncertainties from electromagnetic counterpart selection effects in gravitational-wave standard siren measurements.

Findings

Formalism reduces systematic bias to below 1% with 200 observations

Simulation shows effective mitigation of counterpart selection bias

Method applicable to various electromagnetic emission models

Abstract

The disagreement in the Hubble constant measured by different cosmological probes highlights the need for a better understanding of the observations or new physics. The standard siren method, a novel approach using gravitational-wave observations to determine the distance to binary mergers, has great potential to provide an independent measurement of the Hubble constant and shed light on the tension in the next few years. To realize this goal, we must thoroughly understand the sources of potential systematic bias of standard sirens. Among the known sources of systematic uncertainties, selection effects originating from electromagnetic counterpart observations of gravitational-wave sources may dominate the measurements with percent-level bias and no method to mitigate this effect is currently established. In this Letter, we develop a new formalism to mitigate the counterpart selection effect. We show that our formalism can reduce the systematic uncertainty of standard siren Hubble constant measurement to less than the statistical uncertainty with a simulated population of 200 observations ($\lesssim 1\%$) for a realistic electromagnetic emission model. We conclude with how to apply our formalism to different electromagnetic emissions and observing scenarios.