We describe directed searches for continuous gravitational waves in data from the sixth LIGO science data run. The targets were nine young supernova remnants not associated with pulsars; eight of the ...remnants are associated with non-pulsing suspected neutron stars. One target's parameters are uncertain enough to warrant two searches, for a total of ten. Each search covered a broad band of frequencies and first and second frequency derivatives for a fixed sky direction. The searches coherently integrated data from the two LIGO interferometers over time spans from 5.3-25.3 days using the matched-filtering F-statistic. We found no credible gravitational-wave signals. We set 95% confidence upper limits as strong (low) as \(4\times10^{-25}\) on intrinsic strain, \(2\times10^{-7}\) on fiducial ellipticity, and \(3\times10^{-6}\) on r-mode amplitude. These beat the indirect limits from energy conservation and are within the range of theoretical predictions for neutron-star ellipticities and r-mode amplitudes.
We describe directed searches for continuous gravitational waves from sixteen well localized candidate neutron stars assuming none of the stars has a binary companion. The searches were directed ...toward fifteen supernova remnants and Fomalhaut~b, an extrasolar planet candidate which has been suggested to be a nearby old neutron star. Each search covered a broad band of frequencies and first and second time derivatives. After coherently integrating spans of data from the first Advanced LIGO observing run of 3.5--53.7 days per search, applying data-based vetoes and discounting known instrumental artifacts, we found no astrophysical signals. We set upper limits on intrinsic gravitational wave strain as strict as \(1\times10^{-25}\), on fiducial neutron star ellipticity as strict as \(2\times10^{-9}\), and on fiducial \(r\)-mode amplitude as strict as \(3\times10^{-8}\).
We present results on the mass, spin, and redshift distributions with phenomenological population models using the ten binary black hole mergers detected in the first and second observing runs ...completed by Advanced LIGO and Advanced Virgo. We constrain properties of the binary black hole (BBH) mass spectrum using models with a range of parameterizations of the BBH mass and spin distributions. We find that the mass distribution of the more massive black hole in such binaries is well approximated by models with no more than 1% of black holes more massive than \(45\,M_\odot\), and a power law index of \(\alpha = {1.3}^{+1.4}_{-1.7}\) (90% credibility). We also show that BBHs are unlikely to be composed of black holes with large spins aligned to the orbital angular momentum. Modelling the evolution of the BBH merger rate with redshift, we show that it is at or increasing with redshift with 93% probability. Marginalizing over uncertainties in the BBH population, we find robust estimates of the BBH merger rate density of \(R = {53.2}^{+55.8}_{-28.2}\) Gpc\(^{-3}\) yr\(^{-1}\) (90% credibility). As the BBH catalog grows in future observing runs, we expect that uncertainties in the population model parameters will shrink, potentially providing insights into the formation of black holes via supernovae, binary interactions of massive stars, stellar cluster dynamics, and the formation history of black holes across cosmic time.
Phys. Rev. Lett. 125, 101102 (2020) On May 21, 2019 at 03:02:29 UTC Advanced LIGO and Advanced Virgo observed a
short duration gravitational-wave signal, GW190521, with a three-detector
network ...signal-to-noise ratio of 14.7, and an estimated false-alarm rate of 1
in 4900 yr using a search sensitive to generic transients. If GW190521 is from
a quasicircular binary inspiral, then the detected signal is consistent with
the merger of two black holes with masses of $85^{+21}_{-14} M_{\odot}$ and
$66^{+17}_{-18} M_{\odot}$ (90 % credible intervals). We infer that the primary
black hole mass lies within the gap produced by (pulsational) pair-instability
supernova processes, and has only a 0.32 % probability of being below $65
M_{\odot}$. We calculate the mass of the remnant to be $142^{+28}_{-16}
M_{\odot}$, which can be considered an intermediate mass black hole (IMBH). The
luminosity distance of the source is $5.3^{+2.4}_{-2.6}$ Gpc, corresponding to
a redshift of $0.82^{+0.28}_{-0.34}$. The inferred rate of mergers similar to
GW190521 is $0.13^{+0.30}_{-0.11}\,\mathrm{Gpc}^{-3}\,\mathrm{yr}^{-1}$.
We report the observation of a compact binary coalescence involving a 22.2 -
24.3 $M_{\odot}$ black hole and a compact object with a mass of 2.50 - 2.67
$M_{\odot}$ (all measurements quoted at the ...90$\%$ credible level). The
gravitational-wave signal, GW190814, was observed during LIGO's and Virgo's
third observing run on August 14, 2019 at 21:10:39 UTC and has a
signal-to-noise ratio of 25 in the three-detector network. The source was
localized to 18.5 deg$^2$ at a distance of $241^{+41}_{-45}$ Mpc; no
electromagnetic counterpart has been confirmed to date. The source has the most
unequal mass ratio yet measured with gravitational waves,
$0.112^{+0.008}_{-0.009}$, and its secondary component is either the lightest
black hole or the heaviest neutron star ever discovered in a double
compact-object system. The dimensionless spin of the primary black hole is
tightly constrained to $\leq 0.07$. Tests of general relativity reveal no
measurable deviations from the theory, and its prediction of higher-multipole
emission is confirmed at high confidence. We estimate a merger rate density of
1-23 Gpc$^{-3}$ yr$^{-1}$ for the new class of binary coalescence sources that
GW190814 represents. Astrophysical models predict that binaries with mass
ratios similar to this event can form through several channels, but are
unlikely to have formed in globular clusters. However, the combination of mass
ratio, component masses, and the inferred merger rate for this event challenges
all current models for the formation and mass distribution of compact-object
binaries.
The LIGO Scientific Collaboration and the Virgo Collaboration have cataloged eleven confidently detected gravitational-wave events during the first two observing runs of the advanced detector era. ...All eleven events were consistent with being from well-modeled mergers between compact stellar-mass objects: black holes or neutron stars. The data around the time of each of these events have been made publicly available through the gravitational-wave open science center. The entirety of the gravitational-wave strain data from the first and second observing runs have also now been made publicly available. There is considerable interest among the broad scientific community in understanding the data and methods used in the analyses. In this paper, we provide an overview of the detector noise properties and the data analysis techniques used to detect gravitational-wave signals and infer the source properties. We describe some of the checks that are performed to validate the analyses and results from the observations of gravitational-wave events. We also address concerns that have been raised about various properties of LIGO-Virgo detector noise and the correctness of our analyses as applied to the resulting data.
Astrophysical Journal Letters 892 (2020) L3 On 2019 April 25, the LIGO Livingston detector observed a compact binary
coalescence with signal-to-noise ratio 12.9. The Virgo detector was also taking
...data that did not contribute to detection due to a low signal-to-noise ratio,
but were used for subsequent parameter estimation. The 90% credible intervals
for the component masses range from 1.12 to 2.52 $M_{\odot}$ (1.45 to 1.88
$M_{\odot}$ if we restrict the dimensionless component spin magnitudes to be
smaller than 0.05). These mass parameters are consistent with the individual
binary components being neutron stars. However, both the source-frame chirp
mass $1.44^{+0.02}_{-0.02} M_{\odot}$ and the total mass
$3.4^{+0.3}_{-0.1}\,M_{\odot}$ of this system are significantly larger than
those of any other known binary neutron star system. The possibility that one
or both binary components of the system are black holes cannot be ruled out
from gravitational-wave data. We discuss possible origins of the system based
on its inconsistency with the known Galactic binary neutron star population.
Under the assumption that the signal was produced by a binary neutron star
coalescence, the local rate of neutron star mergers is updated to $250-2810
\text{Gpc}^{-3}\text{yr}^{-1}$.
We present results from a semicoherent search for continuous gravitational waves from the low-mass X-ray binary Scorpius X-1, using a hidden Markov model (HMM) to track spin wandering. This search ...improves on previous HMM-based searches of LIGO data by using an improved frequency domain matched filter, the \(\mathcal{J}\)-statistic, and by analysing data from Advanced LIGO's second observing run. In the frequency range searched, from \(60\) to \(650\,\mathrm{Hz}\), we find no evidence of gravitational radiation. At \(194.6\,\mathrm{Hz}\), the most sensitive search frequency, we report an upper limit on gravitational wave strain (at 95\% confidence) of \(h_0^{95\%} = 3.47 \times 10^{-25}\) when marginalising over source inclination angle. This is the most sensitive search for Scorpius X-1, to date, that is specifically designed to be robust in the presence of spin wandering.
We present the results of a semicoherent search for continuous gravitational waves from the low-mass X-ray binary Scorpius X-1, using data from the first Advanced LIGO observing run. The search ...method uses details of the modelled, parametrized continuous signal to combine coherently data separated by less than a specified coherence time, which can be adjusted to trade off sensitivity against computational cost. A search was conducted over the frequency range from 25 Hz to 2000 Hz, spanning the current observationally-constrained range of the binary orbital parameters. No significant detection candidates were found, and frequency-dependent upper limits were set using a combination of sensitivity estimates and simulated signal injections. The most stringent upper limit was set at 175 Hz, with comparable limits set across the most sensitive frequency range from 100 Hz to 200 Hz. At this frequency, the 95 pct upper limit on signal amplitude h0 is 2.3e-25 marginalized over the unknown inclination angle of the neutron star's spin, and 8.03e-26 assuming the best orientation (which results in circularly polarized gravitational waves). These limits are a factor of 3-4 stronger than those set by other analyses of the same data, and a factor of about 7 stronger than the best upper limits set using initial LIGO data. In the vicinity of 100 Hz, the limits are a factor of between 1.2 and 3.5 above the predictions of the torque balance model, depending on inclination angle, if the most likely inclination angle of 44 degrees is assumed, they are within a factor of 1.7.
We present results from the first directed search for nontensorial gravitational waves. While general relativity allows for tensorial (plus and cross) modes only, a generic metric theory may, in ...principle, predict waves with up to six different polarizations. This analysis is sensitive to continuous signals of scalar, vector or tensor polarizations, and does not rely on any specific theory of gravity. After searching data from the first observation run of the advanced LIGO detectors for signals at twice the rotational frequency of 200 known pulsars, we find no evidence of gravitational waves of any polarization. We report the first upper limits for scalar and vector strains, finding values comparable in magnitude to previously-published limits for tensor strain. Our results may be translated into constraints on specific alternative theories of gravity.
