[Paper Review] Parameter Estimation Bias From Overlapping Binary Black Hole Events In Second Generation Interferometers

P. Relton, V. Raymond|arXiv (Cornell University)|Mar 30, 2021

Pulsars and Gravitational Waves ResearchPhysics and Astronomy57 references39 citations

TL;DR

This paper investigates parameter estimation bias in second-generation gravitational wave detectors caused by overlapping binary black hole (BBH) mergers. Using analytical and simulation-based methods, it shows that current parameter estimation techniques can reliably distinguish overlapping BBH signals when merger times differ by at least 0.1 seconds or when signal-to-noise ratios are significantly unequal, though bias can still occur even when one signal is below detection threshold.

ABSTRACT

Since the initial detection of Gravitational Waves in 2015, 50 candidate events have been reported by the LIGO-Virgo-KAGRA collaboration. As the current generation of detectors move towards their design sensitivity the rate of these detections will increase. The next generation of detectors are likely to have high enough sensitivities that multiple merging binaries will be visible at the same time. In this paper we show that this is likely to happen before the end of the decade, with the move to the LIGO-Voyager detector. We investigate the situation of overlapping Binary-Black-Hole mergers in these detectors. We find that current parameter estimation techniques are capable of distinguishing the louder of two merging BBH events, without significant bias, when their merger times are not less than $\sim0.1$ seconds apart and when the ratio of the signal-to-noise ratios of the systems is uneven. This region of overlapping parameter space is dependent upon the sky locations of the signals and the relation of those locations to the light travel time between detectors. We also find that, if two signals are highly overlapping, then the recovered set of parameters often show strong evidence of precession. Finally we show that bias can occur even when the signal causing the bias is below the detection threshold.

Motivation & Objective

• To assess the risk of parameter estimation bias due to overlapping BBH signals in second-generation gravitational wave detectors.
• To determine the conditions under which overlapping signals can be reliably distinguished using current parameter estimation techniques.
• To evaluate the impact of signal overlap on spin precession modeling and parameter inference.
• To quantify the probability of overlapping BBH events in upcoming LIGO-Voyager observations.

Proposed method

• Used Poisson statistics to model the probability of overlapping BBH mergers based on merger rates and signal durations.
• Calculated signal-to-noise ratio (SNR) thresholds for detectability using power spectral densities (PSDs) and BNS/BBH range conventions.
• Simulated overlapping BBH waveforms with varying time separations and SNR ratios to test parameter estimation performance.
• Applied Bayesian parameter estimation with precessing waveform models (e.g., PhenomPv2) to infer system parameters from combined signals.
• Assessed bias by comparing recovered parameters to injected true values, focusing on mass, spin, and precession parameters.
• Used the inspiral-range package and detector PSDs to estimate detection ranges and signal durations for different detector configurations (aLIGO, LIGO-Voyager, Einstein Telescope).

Experimental results

Research questions

• RQ1 What is the probability of overlapping BBH mergers in second-generation detectors like LIGO-Voyager?
• RQ2 Under what conditions can current parameter estimation techniques distinguish two overlapping BBH signals without significant bias?
• RQ3 How does signal overlap affect the inference of spin precession in binary black hole systems?
• RQ4 Can bias occur in parameter estimation even when one overlapping signal is below the detection threshold?
• RQ5 How do sky location and baseline delay between detectors influence the detectability of overlapping signals?

Key findings

• Overlapping BBH signals can be reliably distinguished without significant bias when the time separation between mergers is ≥0.1 seconds or when the signal-to-noise ratio ratio between the two signals is unequal.
• The probability of overlapping events in LIGO-Voyager is expected to be non-negligible before the end of the decade, especially as detection rates increase.
• When signals are highly overlapping, parameter estimation often shows strong evidence of spin precession, even if the true signal is non-precessing.
• Bias in parameter estimation can occur even when one signal is below the detection threshold, indicating that undetected overlapping events can still distort results.
• The detectability of overlapping signals depends critically on sky location and the light-travel-time baseline between detectors, affecting the degree of waveform interference.