130 research outputs found
Cell states, fates and reprogramming:insights from neural networks, graphical and computational approaches
Gravitational-wave observations of binary black holes: Effect of non-quadrupole modes
We study the effect of non-quadrupolar modes in the detection and parameter
estimation of gravitational waves (GWs) from non-spinning black-hole binaries.
We evaluate the loss of signal-to-noise ratio and the systematic errors in the
estimated parameters when one uses a quadrupole-mode template family to detect
GW signals with all the relevant modes, for target signals with total masses
and mass ratios . Target
signals are constructed by matching numerical-relativity simulations describing
the late inspiral, merger and ringdown of the binary with
post-Newtonian/effective-one-body waveforms describing the early inspiral. We
find that waveform templates modeling only the quadrupolar modes of the GW
signal are sufficient (loss of detection rate ) for the detection of
GWs with mass ratios using advanced GW observatories. Neglecting the
effect of non-quadrupole modes will introduce systematic errors in the
estimated parameters. The systematic errors are larger than the expected
statistical errors for binaries with large, unequal masses
(), for sky-averaged signal-to-noise ratios
larger than . We provide a summary of the regions in the parameter space
where neglecting non-quadrupole modes will cause unacceptable loss of detection
rates and unacceptably large systematic biases in the estimated parameters.Comment: 11 pages, 9 figures, submitted to Phys. Rev.
Frequency-domain gravitational waves from non-precessing black-hole binaries. I. New numerical waveforms and anatomy of the signal
In this paper we discuss the anatomy of frequency-domain gravitational-wave
signals from non-precessing black-hole coalescences with the goal of
constructing accurate phenomenological waveform models. We first present new
numerical-relativity simulations for mass ratios up to 18 including spins. From
a comparison of different post-Newtonian approximants with numerical-relativity
data we select the uncalibrated SEOBNRv2 model as the most appropriate for the
purpose of constructing hybrid post-Newtonian/numerical-relativity waveforms,
and we discuss how we prepare time-domain and frequency-domain hybrid data
sets. We then use our data together with results in the literature to calibrate
simple explicit expressions for the final spin and radiated energy. Equipped
with our prediction for the final state we then develop a simple and accurate
merger-ringdown-model based on modified Lorentzians in the gravitational wave
amplitude and phase, and we discuss a simple method to represent the low
frequency signal augmenting the TaylorF2 post-Newtonian approximant with terms
corresponding to higher orders in the post-Newtonian expansion. We finally
discuss different options for modelling the small intermediate frequency regime
between inspiral and merger-ringdown. A complete phenomenological model based
on the present work is presented in a companion paper.Comment: 17 pages, 18 figures ,minor edits to tex
Frequency-domain gravitational waves from non-precessing black-hole binaries. II. A phenomenological model for the advanced detector era
We present a new frequency-domain phenomenological model of the
gravitational-wave signal from the inspiral, merger and ringdown of
non-precessing (aligned-spin) black-hole binaries. The model is calibrated to
19 hybrid effective-one-body--numerical-relativity waveforms up to mass ratios
of 1:18 and black-hole spins of ( for equal-mass
systems). The inspiral part of the model consists of an extension of
frequency-domain post-Newtonian expressions, using higher-order terms fit to
the hybrids. The merger-ringdown is based on a phenomenological ansatz that has
been significantly improved over previous models. The model exhibits mismatches
of typically less than 1\% against all 19 calibration hybrids, and an
additional 29 verification hybrids, which provide strong evidence that, over
the calibration region, the model is sufficiently accurate for all relevant
gravitational-wave astronomy applications with the Advanced LIGO and Virgo
detectors. Beyond the calibration region the model produces physically
reasonable results, although we recommend caution in assuming that \emph{any}
merger-ringdown waveform model is accurate outside its calibration region. As
an example, we note that an alternative non-precessing model, SEOBNRv2
(calibrated up to spins of only 0.5 for unequal-mass systems), exhibits
mismatch errors of up to 10\% for high spins outside its calibration region. We
conclude that waveform models would benefit most from a larger number of
numerical-relativity simulations of high-aligned-spin unequal-mass binaries.Comment: 27 pages, 21 figures, Updated coefficients tabl
Testing the validity of the single-spin approximation in inspiral-merger-ringdown waveforms
Gravitational-wave signals from black-hole binaries with nonprecessing spins are described by four parameters—each black hole’s mass and spin. It has been shown that the dominant spin effects can be modeled by a single spin parameter, leading to the development of several three-parameter waveform models. Previous studies indicate that these models should be adequate for gravitational-wave detection. In this paper we focus on the systematic biases that would result from using them to estimate binary parameters, and consider a one-parameter family of configurations at mass ratio 4 and for one choice of effective single spin. We find that for low-mass binaries within that family of configurations, where the observable waveform is dominated by the inspiral, the systematic bias in all physical parameters is smaller than the parameter uncertainty due to degeneracies between the mass ratio and the spins, at least up to signal-to-noise ratios (SNRs) of 50. For higher-mass binaries, where the merger and ringdown make a greater contribution to the observed signal, the bias in the mass ratio is comparable to its uncertainty at SNRs of only ∼30, and the bias in the measurement of the total spin is larger than the uncertainty defined by the 90% confidence region even at an SNR of only 10. Although this bias may be mitigated in future models by a better choice of single-effective-spin parameter, these results suggest that it may be possible to accurately measure both black-hole spins in intermediate-mass binaries
An efficient iterative method to reduce eccentricity in numerical-relativity simulations of compact binary inspiral
We present a new iterative method to reduce eccentricity in black-hole-binary
simulations. Given a good first estimate of low-eccentricity starting momenta,
we evolve puncture initial data for ~4 orbits and construct improved initial
parameters by comparing the inspiral with post-Newtonian calculations. Our
method is the first to be applied directly to the gravitational-wave (GW)
signal, rather than the orbital motion. The GW signal is in general less
contaminated by gauge effects, which, in moving-puncture simulations, limit
orbital-motion-based measurements of the eccentricity to an uncertainty of
, making it difficult to reduce the eccentricity below
this value. Our new method can reach eccentricities below in one or
two iteration steps; we find that this is well below the requirements for GW
astronomy in the advanced detector era. Our method can be readily adapted to
any compact-binary simulation with GW emission, including black-hole-binary
simulations that use alternative approaches, and neutron-star-binary
simulations. We also comment on the differences in eccentricity estimates based
on the strain , and the Newman-Penrose scalar .Comment: 24 pages, 25 figures, pdflatex; v2: minor change
Can we measure individual black-hole spins from gravitational-wave observations?
Measurements of black-hole spins from gravitational-wave observations of black-hole binaries with ground-based detectors are known to be hampered by partial degeneracies in the gravitational-wave phasing: between the two component spins, and between the spins and the binary’s mass ratio, at least for signals that are dominated by the binary’s inspiral. Through the merger and ringdown, however, a different set of degeneracies apply. This suggests the possibility that, if the inspiral, merger and ringdown are all within the sensitive frequency band of a detector, we may be able to break these degeneracies and more accurately measure both spins. In this work we investigate our ability to measure individual spins for nonprecessing binaries, for a range of configurations and signal strengths, and conclude that in general the spin of the larger black hole will be measurable (at best) with observations from Advanced LIGO and Virgo. This implies that in many applications waveform models parameterized by only one effective spin will be sufficient. Our work does not consider precessing binaries or subdominant harmonics, although we provide some arguments why we expect that these will not qualitatively change our conclusions
Land Use and Salinity Drive Changes in SAV Abundance and Community Composition
Conserving and restoring submerged aquatic vegetation (SAV) are key management goals for estuaries worldwide because SAV integrates many aspects of water quality and provides a wide range of ecosystem services. Management strategies are typically focused on aggregated abundance of several SAV species, because species cannot be easily distinguished in remotely sensed data. Human land use and shoreline alteration have been shown to negatively impact SAV abundance, but the effects have varied with study, spatial scale, and location. The differences in reported effects may be partly due to the focus on abundance, which overlooks within-community and among-community dynamics that generate total SAV abundance. We analyzed long-term SAV aerial survey data (1984-2009) and ground observations of community composition (1984-2012) in subestuaries of Chesapeake Bay to integrate variations in abundance with differences in community composition. We identified five communities (mixed freshwater, milfoil-Zannichellia, mixed mesohaline, Zannichellia, and Ruppia-Zostera). Temporal variations in SAV abundance were more strongly related to community identity than to terrestrial stressors, and responses to stressors differed among communities and among species. In one fifth of the subestuaries, the community identity changed during the study, and the probability of such a change was positively related to the prevalence of riprapped shoreline in the subestuary. Mixed freshwater communities had the highest rates of recovery, and this may have been driven by Hydrilla verticillata, which was the single best predictor of SAV recovery rate. Additional species-specific and community-specific research will likely yield better understanding of the factors affecting community identity and SAV abundance, more accurate predictive models, and more effective management strategies
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