Session U13: Connecting Gravitational Wave Observations with Source Properties

R-mode frequencies of slowly rotating relativistic neutron stars with realistic equations of state

The frequencies of r-mode oscillations of rotating neutron stars can be useful for guiding and interpreting gravitational wave and electromagnetic observations. We extend the formalism of Lockitch et al to compute r-mode frequencies for slowly rotating relativistic stars with realistic equations of state. We find that the r-mode frequency ranges from 1.39 to 1.57 times the spin frequency of the star when the relativistic compactness parameter (M/R) is varied over the astrophysically motivated interval 0.11 to 0.31. The results presented here are relevant to the design of gravitational wave and electromagnetic r-mode searches, and following a successful r-mode detection could help constrain the high density equation of state.   

Modeling the dynamics of tidally-interacting binary neutron stars up to merger

In this talk, I will report about recent developments in the numerical and analytical modeling of neutron star mergers dynamics and gravitational radiation. I will discuss a new effective-one-body model that incorporates an enhanced attractive tidal potential motivated by recent analytical advances in the post-Newtonian and gravitational self-force description of relativistic tidal interactions. No fitting parameters are introduced for the description of tidal interaction in the late, strong-field dynamics. The model describes dynamics and waveforms from early inspiral up to merger, captures the tidal amplification effects close to merger, and essentialy agrees with numerical data within their uncertainty. Further, I will discuss quasiuniversal relations that characterize the merger dynamics. The equation of state (and mass ratio) dependency of several binary quantities is fully captured by certain dimensionless tidal coupling constants that parametrize the binary tidal interactions. The quasiuniversality is a property of the conservative dynamics; nontrivial relations emerge as the binary becomes tidally dominated. Some recent results about spinning neutron star mergers in the constant rotational velocity numerical relativity framework will be also mentioned.   

BBH Classification Using Principal Component Analysis

Binary black holes will inspiral, merge and ringdown in the LIGO/VIRGO band for an interesting range of total masses. We present an update on our approach of using Principal Component Analysis to build models of NR BBH waveforms that focus on the merger for generic BBH signals. These models are intended to be used to conduct coarse parameter estimation for gravitational wave burst candidate events. The proposed benefit is a fast, optimized catalog that classifies bulk features in the signal.   

Detection and Measurement of Heavy Black Hole Binaries

The advanced LIGO and Virgo detectors will provide sensitivity to gravitational waves down to frequencies of 10 Hz. The merger frequency of binary black hole (BBH) systems scales inversely with the total mass, meaning that this sensitivity improvement will allow for detection and measurement of more massive binaries. In this study, we used inspiral-merger-ringdown (IMR) waveform models based on the effective-one-body (EOB) formalism that also incorporate higher-order modes of radiation beyond the leading $(2,2)$ mode. We perform Bayesian analysis of massive BBH systems with total masses from $50 \mathrm{M}_{\odot}$ to $500 \mathrm{M}_{\odot}$. We investigate the dependence on total mass of the measurement of the masses of the system and demonstrate the importance of the sub-dominant modes both in detection and measurement. The predominant direction of the degeneracy in mass space changes as the signal power is increasingly dominated by the merger and ringdown portions of the waveform for larger total masses. Including these phases as well as higher-order modes is important for ensuring more complete detection and accurate parameter estimation from massive BBH signals.   

Distinguishing neutron stars from black holes and probing the mass gap with Advanced LIGO/Virgo observations

As the LIGO and Virgo detectors reach their advanced design sensitivities gravitational wave observations will become an indispensable tool for learning about the universe. The mergers of binary systems comprised of compact stellar remnants (black holes and neutron stars) are expected to be the most abundant sources detectable by ground-based interferometric detectors.Advancing our understanding of binary astrophysics has long been recognized as a primary science objective for LIGO and Virgo.The potential for using GW observations as laboratories to study the nature of binary systems, and the underlying population of compact binaries, has been explored for several decades building the signal processing framework needed for the coming rush of data. We assess LIGO/Virgo's capabilities by taking advantage of modern data analysis methods and waveform models which include spin-precession effects to study a large ensemble of plausible GW sources. From this large-scale parameter estimation investigation we make quantitative predictions for how well LIGO and Virgo will be able to distinguish between black holes and neutron stars; we appraise the prospect of using LIGO/Virgo observations to definitively confirm, or reject, the existence of a ``mass gap'' between high-mass neutron stars and low-mass black holes; and we demonstrate the importance of including spin precession effects in our model for the gravitational wave signal.   

A semianalytic Fisher matrix for precessing BH-NS binaries

Gravitational waves from precessing black hole-neutron star (BH-NS) binaries let us constrain that binary's properties: the two masses and BH spin. Robust parameter inference, for example by Markov-Chain Monte Carlo, can directly ascertain how well these parameters can be measured. Still, the Fisher matrix provides valuable insight into what parameters can be measured and why, useful both when interpreting more robust results and when extrapolating what science future detectors and detections may enable. In this talk, we describe how to evaluate, simplify, and understand the Fisher matrix for precessing BH-NS binaries. Building on prior work, we simplify the dynamics and signal using a corotating frame; substitute this representation into the Fisher matrix; and demonstrate how the Fisher matrix arises as a sum over multiple harmonics.   

Parameter estimation on gravitational waves from neutron star binaries with spinning components

As we prepare to enter the advanced-detector era of ground-based gravitational-wave astronomy, it is critical that we understand the abilities and limitations of the analyses we are prepared to conduct. Of the many predicted sources, binary neutron star (BNS) coalescences are paramount; their progenitors have been directly observed, and the advanced detectors will be sensitive to binary mergers up to 400 Mpc away. By simulating detector noise and the gravitational waves from an astrophysically motivated BNS source population, we examine the constraints that can be placed on masses and spins of detectable BNS systems in the early advanced-detector era.