[Paper Review] Capability for detection of GW190521-like binary black holes with TianQin

Shuai Liu, Liang-Gui Zhu+3 more|arXiv (Cornell University)|Oct 11, 2021

Pulsars and Gravitational Waves Research134 references31 citations

TL;DR

This paper evaluates TianQin’s capability to detect GW190521-like intermediate-mass black hole binaries, demonstrating it can resolve up to a dozen such sources with SNR > 8 and precisely localize coalescence times (within 1 s) and sky positions (within 1 deg²). With SNR > 12, TianQin can still detect these massive systems and constrain the Hubble constant to 10% precision, while distinguishing formation channels via orbital eccentricity measurements at 10⁻⁴ relative precision.

ABSTRACT

The detection of GW190521 gains huge attention because it is the most massive binary that LIGO and Virgo ever confidently detected until the release of GWTC-3 (GW190426_190642 is more massive), and it is the first black hole merger whose remnant is believed to be an intermediate mass black hole. Furthermore, the primary black hole mass falls in the black hole mass gap, where the pair-instability supernova prevents the formation of astrophysical black holes in this range. In this paper, we systematically explore the prospect of TianQin on detecting GW190521-like sources. For sources with small orbital eccentricities, (i) TianQin could resolve up to a dozen of sources with signal-to-noise ratio (SNR) larger than 8. Even if the signal-to-noise ratio threshold increases to 12, TianQin could still detect GW190521-like binaries. (ii) The parameters of sources merging within several years would be precisely recovered. The precision of coalescence time and sky localization closes to $1\ { m s}$ and $1\ { m deg^{2}}$ respectively. This indicates that TianQin could provide early warnings for ground-based gravitational waves detectors and electromagnetic telescopes for these sources. Furthermore, TianQin could distinguish the formation channels of these sources by measuring the orbital eccentricities with a relative precision of $10^{-4}$. (iii) TianQin could constrain the Hubble constant with a $10\%$ precision with GW190521-like sources. Finally, for very eccentric GW190521-like sources, although their gravitational wave signal might be too weak for TianQin to detect, even the null detection of TianQin could still present a significant contribution to the understanding of the underlying science.

Motivation & Objective

• Assess TianQin’s detection capability for GW190521-like binary black holes, which are among the most massive and significant for IMBH formation.
• Investigate the precision of parameter estimation for such sources, especially coalescence time and sky localization, to enable early warnings for ground-based detectors and EM telescopes.
• Explore TianQin’s potential to distinguish formation channels via orbital eccentricity measurements, which differ between isolated binary evolution and dynamical processes.
• Evaluate the contribution of these detections to cosmological parameter estimation, particularly the Hubble constant, using GW190521-like events as standard sirens.
• Assess the scientific value of null detections for highly eccentric systems, even when undetectable, in constraining formation models and environmental effects.

Proposed method

• Use a 3PN waveform model with eccentricity to simulate gravitational wave signals from GW190521-like binaries, assuming small orbital eccentricities (e ≲ 0.1) for initial analysis.
• Apply matched filtering with TianQin’s sensitivity curve (from [95]) over a 5-year observation period, assuming a '3 months on, 3 months off' duty cycle and considering both single- and twin-constellation configurations.
• Estimate signal-to-noise ratio (SNR) using the standard matched filter signal-to-noise ratio formula, incorporating the full Fisher information matrix for parameter estimation precision.
• Perform Bayesian parameter estimation using the Fisher matrix approximation to compute uncertainties in coalescence time, sky position, and other parameters.
• Assess Hubble constant constraints by treating GW190521-like sources as standard sirens, using luminosity distance estimates from parameter recovery.
• Evaluate eccentricity measurement precision by computing the relative error on eccentricity using the Fisher matrix, assuming joint observations with future ground-based detectors.

Experimental results

Research questions

• RQ1 How many GW190521-like binary black hole events can TianQin detect with SNR > 8 and SNR > 12?
• RQ2 Can TianQin achieve sub-second timing and sub-degree sky localization precision for coalescing GW190521-like binaries, enabling early warning for ground-based and EM follow-up?
• RQ3 To what extent can TianQin distinguish formation channels of GW190521-like binaries by measuring orbital eccentricities with relative precision ~10⁻⁴?
• RQ4 What is the precision with which TianQin can constrain the Hubble constant using GW190521-like sources as standard sirens?
• RQ5 What scientific value does a null detection of highly eccentric GW190521-like systems have for understanding formation mechanisms and environmental effects?

Key findings

• TianQin can detect up to a dozen GW190521-like binary black hole events with signal-to-noise ratio (SNR) > 8, even under realistic observing conditions with data gaps.
• For sources merging within a few years, TianQin can localize coalescence time with a precision of approximately 1 second and sky position to within 1 deg².
• Even with a higher SNR threshold of 12, TianQin remains capable of detecting GW190521-like binaries, indicating strong sensitivity to the most massive systems.
• TianQin can measure orbital eccentricities with a relative precision of 10⁻⁴, enabling clear distinction between binaries formed via isolated binary evolution (low e) and dynamical processes (measurable e).
• GW190521-like sources can be used as standard sirens to constrain the Hubble constant with a precision of about 10%, based on luminosity distance estimates from parameter recovery.
• Even if highly eccentric GW190521-like systems are undetectable due to weak signals, a null detection by TianQin would still provide significant scientific value by constraining formation models and environmental effects.