15 research outputs found
Systematic errors due to quasi-universal relations in binary neutron stars and their correction for unbiased model selection
Inference of the equation-of-state (EoS) of dense nuclear matter in
neutron-star cores is a principal science goal of X-ray and gravitational-wave
observations of neutron stars. In particular, gravitational-wave observations
provide an independent probe of the properties of bulk matter in neutron star
cores that can then be used to compare with theoretically derived equations of
state. In this paper, we quantify the systematic errors arising from the
application of EoS-independent \emph{quasi-universal relations} in the
estimation of neutron star tidal deformabilities and radii from
gravitational-wave measurements and introduce a strategy to correct for the
systematic biases in the inferred radii. We apply this method to a simulated
population of events expected to be observed by future upgrades of current
detectors and the next-generation of ground-based observatories. We show that
our approach can accurately correct for the systematic biases arising from
approximate universal relations in the mass-radius curves of neutron stars.
Using the posterior distributions of the mass and radius for the simulated
population we infer the underlying EoS with a good degree of precision. Our
method revives the possibility of using the universal relations for rapid
Bayesian model selection of dense matter EoS in gravitational-wave
observations
Constraining runaway dilaton models using joint gravitational-wave and electromagnetic observations
With the advent of gravitational-wave astronomy it has now been possible to
constrain modified theories of gravity that were invoked to explain the dark
energy. In a class of dilaton models, distances to cosmic sources inferred from
electromagnetic and gravitational wave observations would differ due to the
presence of a friction term. In such theories, the ratio of the Newton's
constant to the fine structure constant varies with time. In this paper we
explore the degree to which it will be possible to test such models. If
collocated sources (e.g. supernovae and binary neutron star mergers), but not
necessarily multimessengers, can be identified by electromagnetic telescopes
and gravitational-wave detectors one can probe if light and gravitational
radiation are subject to the same laws of propagation over cosmological
distances. This helps in constraining the variation of Newton's constant
relative to fine-structure constant. The next generation of gravitational wave
detectors, such as the Cosmic Explorer and Einstein Telescope, in tandem with
the Vera Rubin Observatory and gamma ray observatories such as the Fermi Space
Observatory will be able to detect or constrain such variations at the level of
a few parts in 100. We apply this method to GW170817 with distances inferred by
the LIGO and Virgo detectors and the observed Kilonova
Cosmography with bright and Love sirens
Precision cosmology is crucial to understand the different energy components
in the Universe and their evolution through cosmic time. Gravitational wave
sources are standard sirens that can accurately map out distances in the
Universe. Together with the source redshift information, we can then probe the
expansion history of the Universe. We explore the capabilities of various
gravitational-wave detector networks to constrain different cosmological models
while employing separate waveform models for inspiral and post-merger part of
the gravitational wave signal from equal mass binary neutron stars. We consider
two different avenues to measure the redshift of a gravitational-wave source:
first, we examine an electromagnetic measurement of the redshift via either a
kilonova or a gamma ray burst detection following a binary neutron star merger
(the electromagnetic counterpart method); second, we estimate the redshift from
the gravitational-wave signal itself from the adiabatic tides between the
component stars characterized by the tidal Love number, to provide a second
mass-scale and break the mass-redshift degeneracy (the counterpart-less
method). We find that the electromagnetic counterpart method is better suited
to measure the Hubble constant while the counterpart-less method places more
stringent bounds on other cosmological parameters. In the era of
next-generation gravitational-wave detector networks, both methods achieve
sub-percent measurement of the Hubble constant after one year of
observations. The dark matter energy density parameter in the
CDM model can be measured at percent-level precision using the
counterpart method, whereas the counterpart-less method achieves sub-percent
precision. We, however, do not find the postmerger signal to contribute
significantly to these precision measurements
Long-Term Optical Flux and Colour Variability in Quasars
We have used optical V and R band observations from the Massive Compact Halo Object (MACHO) project on a sample of 59 quasars behind the Magellanic clouds to study their long term optical flux and colour variations. These quasars, lying in the redshift range of 0.2 < z < 2.8 and having apparent V band magnitudes between 16.6 and 20.1 mag, have observations ranging from 49 to 1353 epochs spanning over 7.5 yr with frequency of sampling between 2 to 10 days. All the quasars show variability during the observing period. The normalised excess variance (Fvar) in V and R bands are in the range 0.2% < FVvar < 1.6% and 0.1% < FRvar < 1.5% respectively. In a large fraction of the sources, Fvar is larger in the V band compared to the R band. From the z-transformed discrete cross-correlation function analysis, we find that there is no lag between the V and R band variations. Adopting the Markov Chain Monte Carlo (MCMC) approach, and properly taking into account the correlation between the errors in colours and magnitudes, it is found that the majority of sources show a bluer when brighter trend, while a minor fraction of quasars show the opposite behaviour. This is similar to the results obtained from another two independent algorithms, namely the weighted linear least squares fit (FITEXY) and the bivariate correlated errors and intrinsic scatter regression (BCES). However, the ordinary least squares (OLS) fit, normally used in the colour variability studies of quasars, indicates that all the quasars studied here show a bluer when brighter trend. It is therefore very clear that the OLS algorithm cannot be used for the study of colour variability in quasars
The Accuracy of Neutron Star Radius Measurement with the Next Generation of Terrestrial Gravitational-Wave Observatories
In this paper, we explore the prospect for improving the measurement accuracy
of masses and radii of neutron stars. We consider imminent and long-term
upgrades of the Laser Interferometer Gravitational-Wave Observatory (LIGO) and
Virgo, as well as next-generation observatories -- the Cosmic Explorer and
Einstein Telescope. We find that neutron star radius with single events will be
constrained to within roughly 500m with the current generation of detectors and
their upgrades. This will improve to 200m, 100m and 50m with a network of
observatories that contain one, two or three next-generation observatories,
respectively. Combining events in bins of 0.05 solar masses we find that for
stiffer (softer) equations-of-state like ALF2 (APR4), a network of three XG
observatories will determine the radius to within 30m (100m) over the entire
mass range of neutron stars from 1 to 2.0 solar masses (2.2 solar masses),
allowed by the respective equations-of-state. Neutron star masses will be
measured to within 0.5 percent with three XG observatories irrespective of the
actual equation-of-state. Measurement accuracies will be a factor of 4 or 2
worse if the network contains only one or two XG observatories, respectively,
and a factor of 10 worse in the case of networks consisting of Advanced LIGO,
Virgo KAGRA and their upgrades. Tens to hundreds of high-fidelity events
detected by future observatories will allow us to accurately measure the
mass-radius curve and hence determine the dense matter equation-of-state to
exquisite precision
Neutron star-black hole mergers in next generation gravitational-wave observatories
Observations by the current generation of gravitational-wave detectors have
been pivotal in expanding our understanding of the universe. Although tens of
exciting compact binary mergers have been observed, neutron star-black hole
(NSBH) mergers remained elusive until they were first confidently detected in
2020. The number of NSBH detections is expected to increase with sensitivity
improvements of the current detectors and the proposed construction of new
observatories over the next decade. In this work, we explore the NSBH detection
and measurement capabilities of these upgraded detectors and new observatories
using the following metrics: network detection efficiency and detection rate as
a function of redshift, distributions of the signal-to-noise ratios, the
measurement accuracy of intrinsic and extrinsic parameters, the accuracy of sky
position measurement, and the number of early-warning alerts that can be sent
to facilitate the electromagnetic follow-up. Additionally, we evaluate the
prospects of performing multi-messenger observations of NSBH systems by
reporting the number of expected kilonova detections with the Vera C. Rubin
Observatory and the Nancy Grace Roman Space Telescope. We find that as many as
kilonovae can be detected by these two telescopes every year,
depending on the population of the NSBH systems and the equation of state of
neutron stars.Comment: 30 pages, 15 figure
Dark sirens to resolve the Hubble-Lemaître tension
The planned sensitivity upgrades to the LIGO and Virgo facilities could uniquely identify host galaxies of dark sirens—compact binary coalescences without any electromagnetic counterparts—within a redshift of z = 0.1. This is aided by the higher-order spherical harmonic modes present in the gravitational-wave signal, which also improve distance estimation. In conjunction, sensitivity upgrades and higher modes will facilitate an accurate, independent measurement of the host galaxy's redshift in addition to the luminosity distance from the gravitational-wave observation to infer the Hubble–Lemaître constant H 0 to better than a few percent in 5 yr. A possible Voyager upgrade or third-generation facilities would further solidify the role of dark sirens for precision cosmology in the future
Prospects for direct detection of black hole formation in neutron star mergers with next-generation gravitational-wave detectors
A direct detection of black hole formation in neutron star mergers would provide invaluable information about matter in neutron star cores and finite temperature effects on the nuclear equation of state. We study black hole formation in neutron star mergers using a set of
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numerical relativity simulations consisting of long-lived and black-hole-forming remnants. The postmerger gravitational-wave spectrum of a long-lived remnant has greatly reduced power at a frequency
f
greater than
f
peak
, for
f
≳
4
 
 
kHz
, with
f
peak
∈
[
2.5
,
4
]
 
 
kHz
. On the other hand, black-hole-forming remnants exhibit excess power in the same large
f
region and manifest exponential damping in the time domain characteristic of a quasinormal mode. We demonstrate that the gravitational-wave signal from a collapsed remnant is indeed a quasinormal ringing. We report on the opportunity for direct detections of black hole formation with next-generation gravitational-wave detectors such as Cosmic Explorer and Einstein Telescope and set forth the tantalizing prospect of such observations up to a distance of 100 Mpc for an optimally oriented and located source with an SNR of 4
Characterizing Gravitational Wave Detector Networks: From A to Cosmic Explorer
Gravitational-wave observations by the Laser Interferometer
Gravitational-Wave Observatory (LIGO) and Virgo have provided us a new tool to
explore the universe on all scales from nuclear physics to the cosmos and have
the massive potential to further impact fundamental physics, astrophysics, and
cosmology for decades to come. In this paper we have studied the science
capabilities of a network of LIGO detectors when they reach their best possible
sensitivity, called A#, and a new generation of observatories that are factor
of 10 to 100 times more sensitive (depending on the frequency), in particular a
pair of L-shaped Cosmic Explorer observatories (one 40 km and one 20 km arm
length) in the US and the triangular Einstein Telescope with 10 km arms in
Europe. We use a set of science metrics derived from the top priorities of
several funding agencies to characterize the science capabilities of different
networks. The presence of one or two A# observatories in a network containing
two or one next generation observatories, respectively, will provide good
localization capabilities for facilitating multimessenger astronomy and
precision measurement of the Hubble parameter. A network of two Cosmic Explorer
observatories and the Einstein Telescope is critical for accomplishing all the
identified science metrics including the nuclear equation of state,
cosmological parameters, growth of black holes through cosmic history, and make
new discoveries such as the presence of dark matter within or around neutron
stars and black holes, continuous gravitational waves from rotating neutron
stars, transient signals from supernovae, and the production of stellar-mass
black holes in the early universe. For most metrics the triple network of next
generation terrestrial observatories are a factor 100 better than what can be
accomplished by a network of three A# observatories.Comment: 45 pages, 20 figure