106 research outputs found
Observing the dynamics of super-massive black hole binaries with Pulsar Timing Arrays
Pulsar Timing Arrays are a prime tool to study unexplored astrophysical
regimes with gravitational waves. Here we show that the detection of
gravitational radiation from individually resolvable super-massive black hole
binary systems can yield direct information about the masses and spins of the
black holes, provided that the gravitational-wave induced timing fluctuations
both at the pulsar and at the Earth are detected. This in turn provides a map
of the non-linear dynamics of the gravitational field and a new avenue to
tackle open problems in astrophysics connected to the formation and evolution
of super-massive black holes. We discuss the potential, the challenges and the
limitations of these observations.Comment: 5 pages, 1 figur
Early Advanced LIGO binary neutron-star sky localization and parameter estimation
2015 will see the first observations of Advanced LIGO and the start of the
gravitational-wave (GW) advanced-detector era. One of the most promising
sources for ground-based GW detectors are binary neutron-star (BNS)
coalescences. In order to use any detections for astrophysics, we must
understand the capabilities of our parameter-estimation analysis. By simulating
the GWs from an astrophysically motivated population of BNSs, we examine the
accuracy of parameter inferences in the early advanced-detector era. We find
that sky location, which is important for electromagnetic follow-up, can be
determined rapidly (~5 s), but that sky areas may be hundreds of square
degrees. The degeneracy between component mass and spin means there is
significant uncertainty for measurements of the individual masses and spins;
however, the chirp mass is well measured (typically better than 0.1%).Comment: 4 pages, 2 figures. Published in the proceedings of Amaldi 1
Enhancing gravitational wave astronomy with galaxy catalogues
Joint gravitational wave (GW) and electromagnetic (EM) observations, as a key
research direction in multi-messenger astronomy, will provide deep insight into
the astrophysics of a vast range of astronomical phenomena. Uncertainties in
the source sky location estimate from gravitational wave observations mean
follow-up observatories must scan large portions of the sky for a potential
companion signal. A general frame of joint GW-EM observations is presented by a
multi-messenger observational triangle. Using a Bayesian approach to
multi-messenger astronomy, we investigate the use of galaxy catalogue and host
galaxy information to reduce the sky region over which follow-up observatories
must scan, as well as study its use for improving the inclination angle
estimates for coalescing binary compact objects. We demonstrate our method
using a simulated neutron stars inspiral signal injected into simulated
Advanced detectors noise and estimate the injected signal sky location and
inclination angle using the Gravitational Wave Galaxy Catalogue. In this case
study, the top three candidates in rank have , and posterior
probability of being the host galaxy, receptively. The standard deviation of
cosine inclination angle (0.001) of the neutron stars binary using
gravitational wave-galaxy information is much smaller than that (0.02) using
only gravitational wave posterior samples.Comment: Proceedings of the Sant Cugat Forum on Astrophysics. 2014 Session on
'Gravitational Wave Astrophysics
Entropy entrainment and dissipation in superfluid Helium
Building on a general variational framework for multi-fluid dynamics, we
discuss finite temperature effects in superfluids. The main aim is to provide
insight into the modelling of more complex finite temperature superfluid
systems, like the mixed neutron superfluid/proton superconductor that is
expected in the outer core of a neutron star. Our final results can also (to a
certain extent) be used to describe colour-flavour locked quark superconductors
that may be present at the extreme densities in the deep neutron star core. As
a demonstration of the validity of the model, which is based on treating the
excitations in the system as a massless ``entropy'' fluid, we show that it is
formally equivalent to the traditional two-fluid approach for superfluid
Helium. In particular, we highlight the fact that the entropy entrainment
encodes the ``normal fluid density'' of the traditional approach. We also show
how the superfluid constraint of irrotationality reduces the number of
dissipation coefficients in the system. This analysis provides insight into the
more general problem when vortices are present in the superfluid, and we
discuss how the so-called mutual friction force can be accounted for in our
framework. The end product is a hydrodynamic formalism for finite temperature
effects in a single superfluid condensate. This framework can readily be
extended to more complex situations.Comment: revised version, clarifies points regarding entrainment in different
context
Towards a generic test of the strong field dynamics of general relativity using compact binary coalescence
Coalescences of binary neutron stars and/or black holes are amongst the most
likely gravitational-wave signals to be observed in ground based
interferometric detectors. Apart from the astrophysical importance of their
detection, they will also provide us with our very first empirical access to
the genuinely strong-field dynamics of General Relativity (GR). We present a
new framework based on Bayesian model selection aimed at detecting deviations
from GR, subject to the constraints of the Advanced Virgo and LIGO detectors.
The method tests the consistency of coefficients appearing in the waveform with
the predictions made by GR, without relying on any specific alternative theory
of gravity. The framework is suitable for low signal-to-noise ratio events
through the construction of multiple subtests, most of which involve only a
limited number of coefficients. It also naturally allows for the combination of
information from multiple sources to increase one's confidence in GR or a
violation thereof. We expect it to be capable of finding a wide range of
possible deviations from GR, including ones which in principle cannot be
accommodated by the model waveforms, on condition that the induced change in
phase at frequencies where the detectors are the most sensitive is comparable
to the effect of a few percent change in one or more of the low-order
post-Newtonian phase coefficients. In principle the framework can be used with
any GR waveform approximant, with arbitrary parameterized deformations, to
serve as model waveforms. In order to illustrate the workings of the method, we
perform a range of numerical experiments in which simulated gravitational waves
modeled in the restricted post-Newtonian, stationary phase approximation are
added to Gaussian and stationary noise that follows the expected Advanced
LIGO/Virgo noise curves.Comment: 26 pages, 23 figures, Accepted by PR
Robust parameter estimation for compact binaries with ground-based gravitational-wave observations using the LALInference software library
The Advanced LIGO and Advanced Virgo gravitational wave (GW) detectors will
begin operation in the coming years, with compact binary coalescence events a
likely source for the first detections. The gravitational waveforms emitted
directly encode information about the sources, including the masses and spins
of the compact objects. Recovering the physical parameters of the sources from
the GW observations is a key analysis task. This work describes the
LALInference software library for Bayesian parameter estimation of compact
binary signals, which builds on several previous methods to provide a
well-tested toolkit which has already been used for several studies. We show
that our implementation is able to correctly recover the parameters of compact
binary signals from simulated data from the advanced GW detectors. We
demonstrate this with a detailed comparison on three compact binary systems: a
binary neutron star, a neutron star black hole binary and a binary black hole,
where we show a cross-comparison of results obtained using three independent
sampling algorithms. These systems were analysed with non-spinning, aligned
spin and generic spin configurations respectively, showing that consistent
results can be obtained even with the full 15-dimensional parameter space of
the generic spin configurations. We also demonstrate statistically that the
Bayesian credible intervals we recover correspond to frequentist confidence
intervals under correct prior assumptions by analysing a set of 100 signals
drawn from the prior. We discuss the computational cost of these algorithms,
and describe the general and problem-specific sampling techniques we have used
to improve the efficiency of sampling the compact binary coalescence parameter
space
Gravitational Waves From Known Pulsars: Results From The Initial Detector Era
We present the results of searches for gravitational waves from a large selection of pulsars using data from the most recent science runs (S6, VSR2 and VSR4) of the initial generation of interferometric gravitational wave detectors LIGO (Laser Interferometric Gravitational-wave Observatory) and Virgo. We do not see evidence for gravitational wave emission from any of the targeted sources but produce upper limits on the emission amplitude. We highlight the results from seven young pulsars with large spin-down luminosities. We reach within a factor of five of the canonical spin-down limit for all seven of these, whilst for the Crab and Vela pulsars we further surpass their spin-down limits. We present new or updated limits for 172 other pulsars (including both young and millisecond pulsars). Now that the detectors are undergoing major upgrades, and, for completeness, we bring together all of the most up-to-date results from all pulsars searched for during the operations of the first-generation LIGO, Virgo and GEO600 detectors. This gives a total of 195 pulsars including the most recent results described in this paper.United States National Science FoundationScience and Technology Facilities Council of the United KingdomMax-Planck-SocietyState of Niedersachsen/GermanyAustralian Research CouncilInternational Science Linkages program of the Commonwealth of AustraliaCouncil of Scientific and Industrial Research of IndiaIstituto Nazionale di Fisica Nucleare of ItalySpanish Ministerio de Economia y CompetitividadConselleria d'Economia Hisenda i Innovacio of the Govern de les Illes BalearsNetherlands Organisation for Scientific ResearchPolish Ministry of Science and Higher EducationFOCUS Programme of Foundation for Polish ScienceRoyal SocietyScottish Funding CouncilScottish Universities Physics AllianceNational Aeronautics and Space AdministrationOTKA of HungaryLyon Institute of Origins (LIO)National Research Foundation of KoreaIndustry CanadaProvince of Ontario through the Ministry of Economic Development and InnovationNational Science and Engineering Research Council CanadaCarnegie TrustLeverhulme TrustDavid and Lucile Packard FoundationResearch CorporationAlfred P. Sloan FoundationAstronom
Gravitational waves from single neutron stars: an advanced detector era survey
With the doors beginning to swing open on the new gravitational wave
astronomy, this review provides an up-to-date survey of the most important
physical mechanisms that could lead to emission of potentially detectable
gravitational radiation from isolated and accreting neutron stars. In
particular we discuss the gravitational wave-driven instability and
asteroseismology formalism of the f- and r-modes, the different ways that a
neutron star could form and sustain a non-axisymmetric quadrupolar "mountain"
deformation, the excitation of oscillations during magnetar flares and the
possible gravitational wave signature of pulsar glitches. We focus on progress
made in the recent years in each topic, make a fresh assessment of the
gravitational wave detectability of each mechanism and, finally, highlight key
problems and desiderata for future work.Comment: 39 pages, 12 figures, 2 tables. Chapter of the book "Physics and
Astrophysics of Neutron Stars", NewCompStar COST Action 1304. Minor
corrections to match published versio
Swift follow-up observations of candidate gravitational-wave transient events
We present the first multi-wavelength follow-up observations of two candidate
gravitational-wave (GW) transient events recorded by LIGO and Virgo in their
2009-2010 science run. The events were selected with low latency by the network
of GW detectors and their candidate sky locations were observed by the Swift
observatory. Image transient detection was used to analyze the collected
electromagnetic data, which were found to be consistent with background.
Off-line analysis of the GW data alone has also established that the selected
GW events show no evidence of an astrophysical origin; one of them is
consistent with background and the other one was a test, part of a "blind
injection challenge". With this work we demonstrate the feasibility of rapid
follow-ups of GW transients and establish the sensitivity improvement joint
electromagnetic and GW observations could bring. This is a first step toward an
electromagnetic follow-up program in the regime of routine detections with the
advanced GW instruments expected within this decade. In that regime
multi-wavelength observations will play a significant role in completing the
astrophysical identification of GW sources. We present the methods and results
from this first combined analysis and discuss its implications in terms of
sensitivity for the present and future instruments.Comment: Submitted for publication 2012 May 25, accepted 2012 October 25,
published 2012 November 21, in ApJS, 203, 28 (
http://stacks.iop.org/0067-0049/203/28 ); 14 pages, 3 figures, 6 tables;
LIGO-P1100038; Science summary at
http://www.ligo.org/science/Publication-S6LVSwift/index.php ; Public access
area to figures, tables at
https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=p110003
Search for gravitational waves associated with the InterPlanetary Network short gamma ray bursts
We outline the scientific motivation behind a search for gravitational waves
associated with short gamma ray bursts detected by the InterPlanetary Network
(IPN) during LIGO's fifth science run and Virgo's first science run. The IPN
localisation of short gamma ray bursts is limited to extended error boxes of
different shapes and sizes and a search on these error boxes poses a series of
challenges for data analysis. We will discuss these challenges and outline the
methods to optimise the search over these error boxes.Comment: Methods paper; Proceedings for Eduardo Amaldi 9 Conference on
Gravitational Waves, July 2011, Cardiff, U
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