Session W01: Gravitational Wave Detection Methods for LIGO I

Ten new binary black hole mergers in the O3a observing run of Advanced LIGO and Advanced Virgo

We report the detection of ten new binary black hole merger signals in the publicly released data from the the first half of the third observing run of advanced LIGO and advanced Virgo (O3a). The mergers were discovered using an updated version of the search pipeline described in Venumadhav et al. (Phys. Rev. D101, 083030 (2020), arXiv:1904.07214), and are selected according to criteria similar to those in LIGO-Virgo Collaboration (LVC) pipeline. The updated search is sensitive to a larger region of parameter space, applies a parameter prior that accounts for different search volume as a function of intrinsic parameters, and uses a new detection statistic that checks for consistency of signals between the Hanford and Livingston detectors. The parameter inference incorporates data from the Virgo detector. We also confirm and raise the significance of the majority of the events reported in the LVC catalog for O3a (GWTC-2.1). Among our ten new events, we observe interesting astrophysical scenarios including possible neutron star black hole (NSBH) mergers at both extreme and near-unity mass ratio, events with confidently large effective spin parameters in both the positive (aligned) and negative (anti-aligned) directions, and a possible intermediate mass black hole (IMBH) merger with a stellar mass companion.   

Investigating waveform systematics between analytical models.

With the detection of multiple gravitational-wave signals, it is vital to have fast and accurate models to correctly infer the properties of binary systems generating these signals. Following up on our recent waveform systematics marginalization study, we present a comparison between different time-domain effective-one-body models and their corresponding frequency-domain surrogate models.   

Predicting Match to Optimize Numerical Relativity Template Placement

As gravitational wave detectors continue to observe an ever increasing number of merging binaries, it's crucial to have template banks which sufficiently span the parameter space. Unfortunately, numerical relativity simulations, which provide the basis for these template banks, are time consuming and computationally expensive. To mitigate this, we can fill in the parameter space more efficiently by identifying new simulations which will provide the most new information. One approach is to perform simulations which will be as different from existing simulations as possible, within the desired parameter space. A useful measure of this is the match, the noise-weighted inner product between the two waveforms. With the goal of performing new simulations in such a way as to minimize their match with existing waveforms, we train a model to predict the match that any two waveforms will have based on their initial parameters.   

Mountains or molehills? Systematic bias from gravitational wave mis-modeling

Gravitational waves emitted during compact binary coalescence offer a unique way to observe strong gravity systems directly. Models of signals produced by coalescence events, derived from general relativity or modified theories of gravity, are used to extract information from gravitational wave data. However, due to the complexity of the theories and computational time constraints, these models are necessarily approximations. Systematic error - or error in parameter estimation resulting from a mismatch between the approximate model and nature - has been studied in depth over the last decades in the context of gravitational waves. We add to this body of knowledge with an injection and recovery campaign. We seek to understand, in particular, the impact post Newtonian corrections to the gravitational wave phase have on systematic error in parameters recovered from signals produced by inspiraling black hole binaries. We consider injected data of non-spinning binaries as detected by ground-based observatories and recover with models of varying PN order in the phase. We will present the conditions under which the dominant source of error in parameter estimation is systematic rather than statistical.   

Marginalizing over Noise Power Spectrum Uncertainty in Gravitational-Wave Parameter Estimation

The traditional gravitational wave parameter estimation process relies on sequential estimation of noise properties and binary parameters, which assumes the noise variance is perfectly known. In this talk I will describe an analysis that simultaneously models the noise power spectrum and the signal, thus marginalizing over uncertainty in the noise. I will compare the sequential estimation method to the simultaneous method on events from GWTC-2 and discuss the effect on inferred parameters. I will argue that at current sensitivities, noise power spectrum uncertainty is a subdominant effect compared to other sources of uncertainty such as waveform systematics.   

Inferring the charge distribution of black hole events from ringdown data.

The increasing precision of gravitational wave detectors has enabled even more precise tests of general relativity, including spectroscopic tests of black holes through the measurement of their quasinormal modes (QNMs). These spectroscopic tests ideally compare the QNM frequencies to predictions from theories beyond GR, where black holes may be described by deformations to the standard Kerr metric. We previously presented a framework to compute the leading shifts to QNM frequencies for perturbations around such deformed Kerr black holes, with arbitrary spin. We show the results of that method, applied to the Kerr Newman case and infer posterior distributions over the charge of the remnant of GW150914. In addition, we generalize this to a hierarchical model and infer the population charge distribution of the entire population of gravitational wave events   

Characterization of precessional and nutational effects on gravitational waveforms via the introduction of five new parameters.

Binary black holes can emit gravitational waves (GW) during their lifetime. BHs are expected to have non-zero spins and the spins can become misaligned with the orbital angular momentum. This misalignment can induce precession and nutation of the orbital angular momentum around the total angular momentum. These phenomena modify the phase and the amplitude of GW. Efforts are underway to quantify these effects via two spin parameters, χ_{eff ,} χ_p inside Post-Newtonian (PN) templates. However, neither precession nor nutation have been detected. We will try to quantify precession and nutation by introducing five new parameters. We believe these parameters may provide a more complete characterization of the amplitude and frequency of precession and nutation as binaries inspiral through the sensitive band of GW detectors. We introduce the parameters inside a PN template and study the modulation of the GW. Then, we use the Fisher matrix analysis on the precessing templates to assess the detectability of our five parameters and to try and break parameter degeneracies. Finally, we calculate the mismatch between templates, to acquire the minimum signal-to-noise needed to distinguish precession and nutation.

    

Constraining two-spin effects in gravitational-wave data with an augmented definition of the precessing spin parameterχp

Spin precession is a key feature in the dynamics of black-hole binaries predicted by General Relativity. Misalignments between the black-hole spins and the binary’s orbital momentum induce characteristic modulations to the emitted gravitational waves which are intrinsically hard to estimate because they provides a highly subdominant contribution. The most commonly used quantity to track the amount of relativistic precession in current LIGO/Virgo observations is the so-called effective precession parameter χ_p. Here we exploit a recently developed re-definition of χ_p that considers all the variations occurring on the precession timescale, allowing to capture two-spin effects in a consistent fashion. In particular, sources with two precessing spins populate a dedicated region of the parameter space where χ_p>1. Using a large number of software injections in synthetic data, we recover the posterior distribution of such augmented χ_p parameter and identify the regions of the parameter space where present and future gravitational-wave interferometers could detect two-spin effects in black-hole binary data.    

Frequency evolution of gravitational wave signals charaterizing black hole superradiance

An ultralight bosonic field can extract energy from a spinning black hole through superradiance. A boson cloud can thus grow from a single particle in a gravitationally bound state. Once the black hole is maximally spun down, the condition for superradiance is no longer satisfied, and the cloud stops growing. The cloud can then dissipate through gravitational radiation, which in turn may be detected by gravitational wave observations. This suggests it may be possible to use black holes as indirect particle detectors for ultralight bosons (including some dark matter candidates). An accurate waveform model of the gravitational radiation expected would allow us to perform sensitive searches for such new particles. With this end in view, this work outlines a relativistic calculation of the time dependence of the radiation frequency.