11 research outputs found
Gravitational waves from binary neutron stars systems
The first observation of gravitational waves from a merger of binary neutron stars (BNS) along with measurements of electromagnetic counterpart has led the beginning of multi-messenger gravitational wave astronomy. In this thesis, we investigate various gravitational waveform models. These models are employed for extracting source properties from the gravitational wave signal from the BNS merger. We perform parameter estimation studies in order to deduce the systematics among these models. We employ different injection scenarios to understand the biases that occur due to differences in the physics included in different waveform models. We present the construction of hybrid waveforms and discuss their applications as a full waveform, e.g., for validation of other waveform models and to check the performance of the models by performing mismatch calculations and parameter estimation studies where hybrid waveforms used as a substitute for a real signal. Based on the systematics study, we show a few of the waveform models give biased esti- mates of the parameters for specific injection scenarios. We improve those models and present the results of the improved models. In the context of having an accurate yet fast-to-evaluate waveform model, we review reduced-order-modeling techniques and present its application for the multipolar TEOBResum model. Furthermore, to validate and tune analytical models, and to investigate the last few orbits near the merger and after the merger, numerical simulations are inevitable. We evaluate the performance of an initial data generating code, called new SGRID code for BNS systems. With the upcoming advance detectors, it is highly likely that events with extreme source properties will get observed. Therefore, in this thesis, we show preliminary results for numerical simulations of BNS mergers with high spins. We vary equation-of-states (EOSs) and spins to investigate the effects of spin and EOS on the dynamics and gravitational waves
Quasi-5.5PN TaylorF2 approximant for compact binaries: point-mass phasing and impact on the tidal polarizability inference
We derive a point-mass (nonspinning) frequency-domain TaylorF2 phasing
approximant at quasi-5.5 post-Newtonian (PN) accuracy for the gravitational
wave from coalescing compact binaries. The new approximant is obtained by
Taylor-expanding the effective-one-body (EOB) resummed energy and and angular
momentum flux along circular orbits with all the known test-particle
information up to 5.5PN. The -- yet uncalculated -- terms at 4PN order and
beyond entering both the energy flux and the energy are taken into account as
free parameters and then set to zero. We compare the quasi-5.5PN and 3.5PN
approximants against full EOB waveforms using gauge-invariant phasing
diagnostics , where is the
dimensionless gravitational-wave frequency. The quasi-5.5PN phasing is found to
be systematically closer to the EOB one than the 3.5PN one. Notably, the
quasi-5.5PN (3.5PN) approximant accumulates a EOBPN dephasing of
rad (rad) up to frequency , 6 orbits to merger, (, 2 orbits to
merger) for a fiducial binary neutron star system. We explore the performance
of the quasi-5.5PN approximant on the measurement of the tidal polarizability
parameter using injections of EOB waveforms hybridized with
numerical relativity merger waveforms. We prove that the quasi-5.5PN point-mass
approximant augmented with 6PN-accurate tidal terms allows one to reduce (and
in many cases even eliminate) the biases in the measurement of
that are instead found when the standard 3.5PN point-mass baseline is used.
Methodologically, we demonstrate that the combined use of analysis
and of the Bayesian parameter estimation offers a new tool to investigate the
impact of systematics on gravitational-wave inference.Comment: 13 pages, 7 figures, submitted to Phys. Rev.
Improving the NRTidal model for binary neutron star systems
Accurate and fast gravitational waveform (GW) models are essential to extract
information about the properties of compact binary systems that generate GWs.
Building on previous work, we present an extension of the NRTidal model for
binary neutron star (BNS) waveforms. The upgrades are: (i) a new closed-form
expression for the tidal contribution to the GW phase which includes further
analytical knowledge and is calibrated to more accurate numerical relativity
data than previously available; (ii) a tidal correction to the GW amplitude;
(iii) an extension of the spin-sector incorporating equation-of-state-dependent
finite size effects at quadrupolar and octupolar order; these appear in the
spin-spin tail terms and cubic-in-spin terms, both at 3.5PN. We add the new
description to the precessing binary black hole waveform model IMRPhenomPv2 to
obtain a frequency-domain precessing binary neutron star model. In addition, we
extend the SEOBNRv4_ROM and IMRPhenomD aligned-spin binary black hole waveform
models with the improved tidal phase corrections. Focusing on the new
IMRPhenomPv2_NRTidalv2 approximant, we test the model by comparing with
numerical relativity waveforms as well as hybrid waveforms combining tidal
effective-one-body and numerical relativity data. We also check consistency
against a tidal effective-one-body model across large regions of the BNS
parameter space.Comment: Accepted manuscrip
Relevance of tidal effects and post-merger dynamics for binary neutron star parameter estimation
Measurements of the properties of binary neutron star systems from
gravitational-wave observations require accurate theoretical models for such
signals. However, current models are incomplete, as they do not take into
account all of the physics of these systems: some neglect possible tidal
effects, others neglect spin-induced orbital precession, and no existing model
includes the post-merger regime consistently. In this work, we explore the
importance of two physical ingredients: tidal interactions during the inspiral
and the imprint of the post-merger stage. We use complete
inspiral--merger--post-merger waveforms constructed from a tidal
effective-one-body approach and numerical-relativity simulations as signals
against which we perform parameter estimates with waveform models of standard
LIGO-Virgo analyses. We show that neglecting tidal effects does not lead to
appreciable measurement biases in masses and spin for typical observations
(small tidal deformability and signal-to-noise ratio 25). However, with
increasing signal-to-noise ratio or tidal deformability there are biases in the
estimates of the binary parameters. The post-merger regime, instead, has no
impact on gravitational-wave measurements with current detectors for the
signal-to-noise ratios we consider
Gravitational waves and mass ejecta from binary neutron star mergers: Effect of the spin orientation
We continue our study of the binary neutron star parameter space by
investigating the effect of the spin orientation on the dynamics, gravitational
wave emission, and mass ejection during the binary neutron star coalescence. We
simulate seven different configurations using multiple resolutions to allow a
reasonable error assessment. Due to the particular choice of the setups, five
configurations show precession effects, from which two show a precession
("wobbling") of the orbital plane, while three show a "bobbing" motion, i.e.,
the orbital angular momentum does not precess, while the orbital plane moves
along the orbital angular momentum axis. Considering the ejection of mass, we
find that precessing systems can have an anisotropic mass ejection, which could
lead to a final remnant kick of for the studied systems.
Furthermore, for the chosen configurations, antialigned spins lead to larger
mass ejecta than aligned spins, so that brighter electromagnetic counterparts
could be expected for these configurations. Finally, we compare our simulations
with the precessing, tidal waveform approximant IMRPhenomPv2_NRTidalv2 and find
good agreement between the approximant and our numerical relativity waveforms
with phase differences below 1.2 rad accumulated over the last 16
gravitational wave cycles.Comment: 18 pages, 16 figure
CoRe database of binary neutron star merger waveforms
We present the Computational Relativity CoRe collaboration's public database of gravitational waveforms from binary neutron star mergers. The database currently contains 367 waveforms from numerical simulations that are consistent with general relativity and that employ constraint satisfying initial data in hydrodynamical equilibrium. It spans 164 physically distinct configuration with different binary parameters (total binary mass, mass-ratio, initial separation, eccentricity, and stars' spins) and simulated physics. Waveforms computed at multiple grid resolutions and extraction radii are provided for controlling numerical uncertainties. We also release an exemplary set of 18 hybrid waveforms constructed with a state-of-art effective-one-body model spanning the frequency band of advanced gravitational-wave detectors. We outline present and future applications of the database to gravitational-wave astronomy
Laying the foundation of the effective-one-body waveform models SEOBNRv5: improved accuracy and efficiency for spinning non-precessing binary black holes
We present SEOBNRv5HM, a more accurate and faster inspiral-merger-ringdown
gravitational waveform model for quasi-circular, spinning, nonprecessing binary
black holes within the effective-one-body (EOB) formalism. Compared to its
predecessor, SEOBNRv4HM, the waveform model i) incorporates recent high-order
post- Newtonian results in the inspiral, with improved resummations, ii)
includes the gravitational modes (l, |m|) = (3, 2), (4, 3), in addition to the
(2, 2), (3, 3), (2, 1), (4, 4), (5, 5) modes already implemented in SEOBNRv4HM,
iii) is calibrated to larger mass-ratios and spins using a catalog of 442
numerical-relativity (NR) simulations and 13 additional waveforms from
black-hole perturbation theory, iv) incorporates information from second-order
gravitational self-force (2GSF) in the nonspinning modes and radiation-reaction
force. Computing the unfaithfulness against NR simulations, we find that for
the dominant (2, 2) mode the maximum unfaithfulness in the total mass range
is below for 90% of the cases (38% for
SEOBNRv4HM). When including all modes up to l = 5 we find 98% (49%) of the
cases with unfaithfulness below , while these numbers reduce
to 88% (5%) when using SEOBNRv4HM. Furthermore, the model shows improved
agreement with NR in other dynamical quantities (e.g., the angular momentum
flux and binding energy), providing a powerful check of its physical
robustness. We implemented the waveform model in a high-performance Python
package (pySEOBNR), which leads to evaluation times faster than SEOBNRv4HM by a
factor 10 to 50, depending on the configuration, and provides the flexibility
to easily include spin-precession and eccentric effects, thus making it the
starting point for a new generation of EOBNR waveform models (SEOBNRv5) to be
employed for upcoming observing runs of the LIGO-Virgo-KAGRA detectors
Constructing binary neutron star initial data with high spins, high compactnesses, and high mass ratios
Laying the foundation of the effective-one-body waveform models SEOBNRv5: improved accuracy and efficiency for spinning non-precessing binary black holes
International audienceWe present SEOBNRv5HM, a more accurate and faster inspiral-merger-ringdown gravitational waveform model for quasi-circular, spinning, nonprecessing binary black holes within the effective-one-body (EOB) formalism. Compared to its predecessor, SEOBNRv4HM, the waveform model i) incorporates recent high-order post- Newtonian results in the inspiral, with improved resummations, ii) includes the gravitational modes (l, |m|) = (3, 2), (4, 3), in addition to the (2, 2), (3, 3), (2, 1), (4, 4), (5, 5) modes already implemented in SEOBNRv4HM, iii) is calibrated to larger mass-ratios and spins using a catalog of 442 numerical-relativity (NR) simulations and 13 additional waveforms from black-hole perturbation theory, iv) incorporates information from second-order gravitational self-force (2GSF) in the nonspinning modes and radiation-reaction force. Computing the unfaithfulness against NR simulations, we find that for the dominant (2, 2) mode the maximum unfaithfulness in the total mass range is below for 90% of the cases (38% for SEOBNRv4HM). When including all modes up to l = 5 we find 98% (49%) of the cases with unfaithfulness below , while these numbers reduce to 88% (5%) when using SEOBNRv4HM. Furthermore, the model shows improved agreement with NR in other dynamical quantities (e.g., the angular momentum flux and binding energy), providing a powerful check of its physical robustness. We implemented the waveform model in a high-performance Python package (pySEOBNR), which leads to evaluation times faster than SEOBNRv4HM by a factor 10 to 50, depending on the configuration, and provides the flexibility to easily include spin-precession and eccentric effects, thus making it the starting point for a new generation of EOBNR waveform models (SEOBNRv5) to be employed for upcoming observing runs of the LIGO-Virgo-KAGRA detectors