ABSTRACT
We re-analyse the Laser Interferometer Gravitational-Wave Observatory (LIGO)–Virgo strain data of the 10 binary black hole mergers reported to date and compute the likelihood function in ...terms of chirp mass, mass ratio, and effective spin. We discuss the strong degeneracy between mass ratio and spin for the three lighter events. We use this likelihood and an estimate of the horizon volume as a function of intrinsic parameters to constrain the properties of the population of merging binary black holes. The data disfavour large spins. Typical spins are constrained to $\overline{a} \lesssim 0.4$, even if the underlying population has randomly oriented spins. For aligned spins, the constraints are tighter, with typical spins required to be around $\overline{a}\sim 0.1$ and have comparable dispersion. We detect no statistically significant tendency towards a positive average spin in the direction of the orbital angular momentum. We put an upper limit on the fraction of systems where the secondary could have been tidally locked prior to the formation of the black holes (corresponding to merger times shorter than 108 yr) f ≲ 0.3. Four events are consistent with having a maximally spinning secondary, although one only marginally. We confirm previous findings that there is a hint of a cut-off at high mass. The data favour distributions of mass ratios with an average $\overline{q} \gtrsim 0.7$.
We report the detection of new binary black hole merger events in the publicly available data from the second observing run of Advanced LIGO and Advanced Virgo (O2). The mergers were discovered using ...the new search pipeline described in Venumadhav et al. Phys. Rev. D 100, 023011 (2019) and are above the detection thresholds as defined in Abbott et al. (LIGO Scientific and Virgo Collaborations) Phys. Rev. X 9, 031040 (2019).. Three of the mergers (GW170121, GW170304, GW170727) have inferred probabilities of being of astrophysical origin pastro>0.98. The remaining three (GW170425, GW170202, GW170403) are less certain, with pastro ranging from 0.5 to 0.8. The newly found mergers largely share the statistical properties of previously reported events, with the exception of GW170403, the least secure event, which has a highly negative effective spin parameter χeff. The most secure new event, GW170121 (pastro>0.99), is also notable due to its inferred negative value of χeff, which is inconsistent with being positive at the ≈95.8% confidence level. The new mergers nearly double the sample of gravitational wave events reported from O2 and present a substantial opportunity to explore the statistics of the binary black hole population in the Universe. The number of detected events is not surprising since we estimate that the detection volume of our pipeline may be larger than that of other pipelines by as much as a factor of 2 (with significant uncertainties in the estimate). The increase in volume is larger when the constituent detectors of the network have very different sensitivities, as is likely to be the case in current and future runs.
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We perform a statistical inference of the astrophysical population of binary black hole (BBH) mergers observed during the first two observing runs of Advanced LIGO and Advanced Virgo, including ...events reported in the GWTC-1 and IAS catalogs. We derive a novel formalism to fully and consistently account for events of arbitrary significance. We carry out a software injection campaign to obtain a set of mock astrophysical events subject to our selection effects, and use the search background to compute the astrophysical probabilities pastro of candidate events for several phenomenological models of the BBH population. We emphasize that the values of pastro depend on both the astrophysical and background models. Finally, we combine the information from individual events to infer the rate, spin, mass, mass-ratio and redshift distributions of the mergers. The existing population does not discriminate between random spins with a spread in the effective spin parameter, and a small but nonzero fraction of events from tidally torqued stellar progenitors. The mass distribution is consistent with one having a cutoff at ... M⊙ , while the mass ratio favors equal masses; the mean mass ratio q > 0.67 . The rate shows no significant evolution with redshift. We show that the merger rate restricted to BBHs with a primary mass between 20–30 M , and a mass ratio q > 0.5 , and at z ~ 0.2 , is 1.5–5.3 Gpc−3 yr−1 (90% c.l.); these bounds are model independent and a factor of ∼ 3 tighter than that on the local rate of all BBH mergers, and hence are a robust constraint on all progenitor models. Including the events in our catalog increases the Fisher information about the BBH population by ∼ 47 % , and tightens the constraints on population parameters. (ProQuest: ... denotes formula omitted.)
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In this paper, we report on the construction of a new and independent pipeline for analyzing the public data from the first observing run of Advanced LIGO for mergers of compact binary systems. The ...pipeline incorporates different techniques and makes independent implementation choices in all its stages including the search design, the method to construct template banks, the automatic routines to detect bad data segments ("glitches") and to insulate good data from them, the procedure to account for the nonstationary nature of the detector noise, the signal-quality vetoes at the single-detector level and the methods to combine results from multiple detectors. Our pipeline enabled us to identify a new binary black hole merger GW151216 in the public LIGO data. This paper serves as a bird's eye view of the pipeline's important stages. Full details and derivations underlying the various stages will appear in accompanying papers.
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We report a new binary black hole merger in the publicly available LIGO first observing run (O1) data release. The event has a false alarm rate of one per six years in the detector-frame chirp-mass ...range Mdet∈20,40M⊙ in a new independent analysis pipeline that we developed. Our best estimate of the probability that the event is of astrophysical origin is Pastro~0.71. The estimated physical parameters of the event indicate that it is the merger of two massive black holes, Mdet=31−3+2M⊙ with an effective spin parameter, χeff=0.81−0.21+0.15, making this the most highly spinning merger reported to date. It is also among the two highest redshift mergers observed so far. The high aligned spin of the merger supports the hypothesis that merging binary black holes can be created by binary stellar evolution.
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The distribution of effective spin χeff, a parameter that encodes the degree of spin-orbit alignment in a binary system, has been widely regarded as a robust discriminator between the isolated and ...dynamical formation pathways for merging binary black holes. Until the recent release of the GWTC-2 catalog, such tests have yielded inconclusive results due to the small number of events with measurable nonzero spins. In this work, we study the χ eff distribution of the binary black holes detected in the LIGO-Virgo O1–O3a observing runs. Our focus is on the degree to which the χeff distribution is symmetric about χeff = 0 and whether the data provide support for a population of negative- χ eff systems. We find that the χeff distribution is asymmetric at 95% credibility, with an excess of aligned-spin binary systems (χeff >0) over antialigned ones. Moreover, we find that there is no evidence for negative- χeff systems in the current population of binary black holes. Thus, based solely on the χeff distribution, dynamical formation is disfavored as being responsible for the entirety of the observed merging binary black holes, while isolated formation remains viable. We also study the mass distribution of the current binary black hole population, confirming that a single truncated power-law distribution in the primary source-frame mass, m1s, fails to describe the observations. Instead, we find that the preferred models have a steep feature at m1s ~ 40 M⊙ consistent with a step and an extended, shallow tail to high masses.
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We introduce an algorithm for placing template waveforms for the search of compact binary mergers in gravitational wave interferometer data. We exploit the smooth dependence of the amplitude and ...unwrapped phase of the frequency-domain waveform on the parameters of the binary. We group waveforms with similar amplitude profiles and perform a singular value decomposition of the phase profiles to obtain an orthonormal basis for the phase functions. The leading basis functions span a lower-dimensional linear space in which the unwrapped phase of any physical waveform is well approximated. The optimal template placement is given by a regular grid in the space of linear coefficients. The algorithm is applicable to any frequency-domain waveform model and detector sensitivity curve. It is computationally efficient and requires little tuning. Applying this method, we construct a set of template banks suitable for the search of aligned-spin binary neutron star, neutron-star–black-hole (NSBH) and binary black hole mergers in LIGO-Virgo data.
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We perform a detailed parameter estimation study of binary black hole merger events reported by Zackay et al. Phys. Rev. D 100, 023007 (2019) and Venumadhav et al. Phys. Rev. D 101, 083030 (2020). ...These are some of the faintest signals reported so far, and hence, relative to the loud events in the GWTC-1 catalog B. P. Abbott et al. (LIGO Scientific and Virgo Collaborations), Phys. Rev. X 9, 031040 (2019), the data should have lesser constraining power on their intrinsic parameters. Hence we examine the robustness of parameter inference to choices made in the analysis, as well as any potential systematics. We check the impact of different methods of estimating the noise power spectral density, different waveform models, and different priors for the compact object spins. For most of the events, the resulting differences in the inferred values of the parameters are much smaller than their statistical uncertainties. The estimation of the effective spin parameter χeff, i.e., the projection of the mass-weighted total spin along the angular momentum, can be sensitive to analysis choices for two of the sources with the largest effective spin magnitudes, GW151216 and GW170403. The primary differences arise from using a 3D isotropic spin prior: the tails of the posterior distributions should be interpreted with care and due consideration of the other data analysis choices.
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This review provides a conceptual and technical survey of methods for parameter estimation of gravitational-wave signals in ground-based interferometers such as Laser Interferometer ...Gravitational-Wave Observatory (LIGO) and Virgo. We introduce the framework of Bayesian inference and provide an overview of models for the generation and detection of gravitational waves from compact binary mergers, focusing on the essential features that are observable in the signals. Within the traditional likelihood-based paradigm, we describe various approaches for enhancing the efficiency and robustness of parameter inference. This includes techniques for accelerating likelihood evaluations, such as heterodyne/relative binning, reduced-order quadrature, multibanding, and interpolation. We also cover methods to simplify the analysis to improve convergence, via reparameterization, importance sampling, and marginalization. We end with a discussion of recent developments in the application of likelihood-free (simulation-based) inference methods to gravitational-wave data analysis.
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