Characterization of low-significance gravitational-wave compact binary sources

Abstract

Advanced LIGO and Virgo have so far detected gravitational waves from 10 binary black hole mergers (BBH) and 1 binary neutron star merger (BNS). In the future, we expect the detection of many more marginal sources, since compact binary coalescences detectable by advanced ground-based instruments are roughly distributed uniformly in comoving volume. In this paper we simulate weak signals from compact binary coalescences of various morphologies and optimal network signal-to-noise ratios (henceforth SNRs), and analyze if and to which extent their parameters can be measured by advanced LIGO and Virgo in their third observing run. We show that subthreshold binary neutron stars, with SNRs below 12 (10) yield uncertainties in their sky position larger than 400 (700) deg 2 (90% credible interval). The luminosity distance, which could be used to measure the Hubble constant with standard sirens, has relative uncertainties larger than 40% for BNSs and neutron star black hole mergers. For sources with SNRs below 8, it is not uncommon that the extrinsic parameters, sky position and distance, cannot be measured. Next, we look at the intrinsic parameters, masses and spins. We show that the detector-frame chirp mass can sometimes be measured with uncertainties below 1% even for sources at SNRs of 6, although multimodality is not uncommon and can significantly broaden the posteriors. The effective inspiral spin is best measured for neutron star black hole mergers, for which the uncertainties can be as low as ∼ 0.08 (∼ 0.2) at SNR 12 (8). The uncertainty is higher for systems with comparable component masses or lack of spin precession. * ywh@mit.edu † salvatore.vitale@ligo.org possibility of multimessenger observations. This has been spectacularly shown with the joint detection of GW and EM signals from the BNS source GW170817 [30]. The host of GW170817 was identified, together with radiation in the whole EM spectrum, from radio to γ-rays [30][31][32][33][34]. The science output of this discovery is too rich to be fully described here. We thus only mention a few highlights. GW170817 was used to set constraints on the equation of state of neutron stars [35], search for evidence of p-g modes [36] and put bounds on the component neutron star masses and spins [13]. The EM data confirmed the connection between short gamma-ray bursts and BNS sources, lead to the observation of the kilonova, and yielded insights on the details of the EM emission [37][38][39][40]. Information from both the GW and the EM sides was used to measure the Hubble constant in a way that is independent of the cosmic distance ladder [41]. As more BNSs are detected in the next years, we will be able to gain a more solid understanding of the properties of compact binaries, their progenitors, and the electromagnetic radiation they emit.Given the current detections, it is possible to estimate the local merger rates of binary neutron stars [12] and binary black holes [5,8,15]. Neutron star black hole mergers (NSBHs) are also promising sources, but have not been detected...

GWTC-3: Compact Binary Coalescences Observed by LIGO and Virgo During the Second Part of the Third Observing Run

“…Due to the correlations between masses and spins [138][139][140], multimodality in mass distributions may also translate to multiple peaks in the effective inspiral spin distribution. Multimodality can arise due to: the complexity of the likelihood surface when using waveform models that include higher-order multipole moments [19,[141][142][143] and precession [144,145], noise fluctuations for quiet signals [146], the presence of glitches [147][148][149], or there being multiple overlapping signals in the data (which is unlikely given O3 sensitivity) [150]. Therefore, multimodality is expected in a few cases.…”

Search for gravitational-wave signals associated with gamma-ray bursts during the second observing run of Advanced LIGO and Advanced Virgo

“…The largest BF was 2.08 in the case of 170726249 (p-value = 0.0262). We also note that, in the absence of a signal with moderate signal-to-noise ratio (SNR), inferred posterior probability distributions will be prior dominated, and in the presence of non-Gaussian noise fluctuations parameter estimation methods may return broad posteriors with multiple peaks, even for typically well constrained parameters such as the chirp mass (Huang et al 2018). We observe these posterior features in our follow-up analyses as noted in Table 2.…”

“…Bayes factors (BFs) quantify the Bayesian odds ratio between the hypothesis that there is a coherent NS binary merger signal in the data versus the hypothesis that the data contain only instrumental noise, which may be purely Gaussian or include incoherent non-Gaussianities (see Equation 1 and accompanying discussion in Isi et al 2018). At low signal-to-noise ratio (SNR), inferred posterior probability distributions tend to be prior dominated and in the presence of non-Gaussian noise fluctuations may exhibit multiple peaks, even for typically well constrained parameters such as the chirp mass (Huang et al 2018). We report here ρ, the network matched filter SNR corresponding to the maximum of the likelihood as estimated by LALInference.…”

Measuring eccentricity of binary black holes in GWTC-1 by using inspiral-only waveform

“…We have also investigated the relationship between the 90% credible interval and the signal-to-noise ratio of the detector network (Huang et al 2018). The result is plotted in the Figure 4.…”

“…The simulated data used here is the same as those in the Figure 3. Huang et al (2018) from the prior distributions. This is better to test the general capability of our method.…”