174 research outputs found
The LISA Gravitational Wave Foreground: A Study of Double White Dwarfs
Double white dwarfs are expected to be a source of confusion-limited noise
for the future gravitational wave observatory LISA. In a specific frequency
range, this 'foreground noise' is predicted to rise above the instrumental
noise and hinder the detection of other types of signals, e.g., gravitational
waves arising from stellar mass objects inspiraling into massive black holes.
In many previous studies only detached populations of compact object binaries
have been considered in estimating the LISA gravitational wave foreground
signal. Here, we investigate the influence of compact object detached and
Roche-Lobe Overflow Galactic binaries on the shape and strength of the LISA
signal. Since >99% of remnant binaries which have orbital periods within the
LISA sensitivity range are white dwarf binaries, we consider only these
binaries when calculating the LISA signal. We find that the contribution of
RLOF binaries to the foreground noise is negligible at low frequencies, but
becomes significant at higher frequencies, pushing the frequency at which the
foreground noise drops below the instrumental noise to >6 mHz. We find that it
is important to consider the population of mass transferring binaries in order
to obtain an accurate assessment of the foreground noise on the LISA data
stream. However, we estimate that there still exists a sizeable number (~11300)
of Galactic double white dwarf binaries which will have a signal-to-noise ratio
>5, and thus will be potentially resolvable with LISA. We present the LISA
gravitational wave signal from the Galactic population of white dwarf binaries,
show the most important formation channels contributing to the LISA disc and
bulge populations and discuss the implications of these new findings.Comment: ApJ accepted. 28 pages, 11 figures (low resolution), 5 tables, some
new references and changed content since last astro-ph versio
Selection effects in resolving Galactic binaries with LISA
Using several realisations of the Galactic population of close white dwarf
binaries, we have explored the selection bias for resolved binaries in the LISA
data stream. We have assumed a data analysis routine that is capable of
identifying binaries that have a signal to noise ratio of at least 5 above a
confusion foreground of unresolved binaries. The resolved population of
binaries is separated into a subpopulation over 1000 binaries that have a
measureable chirp and another subpopulation over 20,000 binaries that do not.
As expected, the population of chirping binaries is heavily skewed toward high
frequency, high chirp mass systems, with little or no preference for nearby
systems. The population of non-chirping binaries is still biased toward
frequencies above about 1 mHz. There is an overabundance of higher mass systems
than is present in the complete Galactic population.Comment: 9 pages, 8 figures, GWDAW 11 proceeding
A search for periodic gravitational waves from three recycled pulsars using the AURIGA detector
Aims.We report on a search for continuous gravitational wave emission from three recycled radio pulsars, performed by using the data of the resonant detector AURIGA. Given the spin rate of the selected targets - the isolated pulsar PSR J1939+2134 and the binary pulsars PSR J0024-7204J and PSR J0218+4232 - the expected frequency of the emitted gravitational waves falls in the high sensitivity range of the detector. Methods.The main topic is the method, meaning that the statistical analysis is performed by implementing a slightly modified version of the Feldman and Cousins Unified Approach. Results.By using ephemerides provided by suitable radio observations of the targets, we were able to demodulate the Doppler shifts within a coherence time of 1 day, and then incoherently sum 10 daily spectra collected from December 8th to December 17th, 2006. We have found upper limits on the gravitational wave amplitudes in the order of a few units of 10-23 at 90% Confidence Level (C.L.), which translate to limits in the ellipticity of the targeted pulsars of ε \u3c 10 -4 at 90% C.L. Conclusions. The same framework can then be applied to data coming from most sensitive experiments as VIRGO or LIGO; moreover, an application to recently discovered transients in X-ray pulsars is discussed. © 2009 ESO
The origin of the first neutron star -- neutron star merger
The first neutron star-neutron star (NS-NS) merger was discovered on August
17, 2017 through gravitational waves (GW170817) and followed with
electromagnetic observations. This merger was detected in an old elliptical
galaxy with no recent star formation. We perform a suite of numerical
calculations to understand the formation mechanism of this merger. We probe
three leading formation mechanisms of double compact objects: classical
isolated binary star evolution, dynamical evolution in globular clusters and
nuclear cluster formation to test whether they are likely to produce NS-NS
mergers in old host galaxies. Our simulations with optimistic assumptions show
current NS-NS merger rates at the level of 10^-2 yr^-1 from binary stars, 5 x
10^-5 yr^-1 from globular clusters and 10^-5 yr^-1 from nuclear clusters for
all local elliptical galaxies (within 100 Mpc^3). These models are thus in
tension with the detection of GW170817 with an observed rate 1.5 yr^-1 (per 100
Mpc^3; LIGO/Virgo estimate). Our results imply that either (i) the detection of
GW170817 by LIGO/Virgo at their current sensitivity in an elliptical galaxy is
a statistical coincidence; or that (ii) physics in at least one of our three
models is incomplete in the context of the evolution of stars that can form
NS-NS mergers; or that (iii) another very efficient (unknown) formation channel
with a long delay time between star formation and merger is at play.Comment: A&A: accepte
A Search For Periodic Gravitational Waves From Three Recycled Pulsars Using The Auriga Detector - An Implementation Of A Modified Version Of The Unified Approach Method
We report on a search for continuous gravitational wave emission from three recycled radio pulsars, performed by using the data of the resonant detector AURIGA. Given the spin rate of the selected targets – the isolated pulsar PSR J1939+2134 and the binary pulsars PSR J0024-7204J and PSR J0218+4232 – the expected frequency of the emitted gravitational waves falls in the high sensitivity range of the detector
On the formation and evolution of the first Be star in a black hole binary MWC 656
We find that the formation of MWC 656 (the first Be binary containing a black
hole) involves a common envelope phase and a supernova explosion. This result
supports the idea that a rapidly rotating Be star can emerge out of a common
envelope phase, which is very intriguing because this evolutionary stage is
thought to be too fast to lead to significant accretion and spin up of the B
star.
We predict of B BH binaries to currently reside in the Galactic
disk, among which around contain a Be star, but there is only a small
chance to observe a system with parameters resembling MWC 656. If MWC 656 is
representative of intrinsic Galactic Be BH binary population, it may indicate
that standard evolutionary theory needs to be revised. This would pose another
evolutionary problem in understanding BH binaries, with BH X-ray Novae
formation issue being the prime example.
The future evolution of MWC 656 with a M black hole and
with a M main sequence companion on a day orbit
may lead to the formation of a coalescing BH-NS system. The estimated Advanced
LIGO/Virgo detection rate of such systems is up to yr. This
empirical estimate is a lower limit as it is obtained with only one particular
evolutionary scenario, the MWC 656 binary. This is only a third such estimate
available (after Cyg X-1 and Cyg X-3), and it lends additional support to the
existence of so far undetected BH--NS binaries.Comment: revised and extended version after MNRAS review 17 pages, 10 figure
LISA Sources in Globular Clusters
Globular clusters house a population of compact binaries that will be
interesting gravitational wave sources for LISA. We provide estimates for the
numbers of sources of several categories and discuss the sensitivity of LISA to
detecting these sources. The estimated total number of detectable sources
ranges from about 10 to about 1000 with gravitational wave frequencies above 1
mHz. These sources are typically undetectable by any other means and thus offer
an opportunity for doing true gravitational-wave astronomy. The detection of
these sources would provide information about both binary star evolution and
the dynamics of globular clusters.Comment: Contribution to Proceedings of 3rd LISA Symposium 7 pages, added
reference
Gravitational Radiation from Pulsating White Dwarfs
Rotating white dwarfs undergoing quasi-radial oscillations can emit
gravitational radiation in a frequency range from 0.1 - 0.3 Hz. Assuming that
the energy source for the gravitational radiation comes from the oblateness of
the white dwarf induced by the rotation, the strain amplitude is found to be
\sim 10^{-27} for a white dwarf at \sim 50 pc. The galactic population of these
sources is estimated to be \sim 10^7, and may produce a confusion limited
foreground for proposed advanced detectors in the frequency band between
space-based and ground-based interferometers. Nearby oscillating white dwarfs
may provide a clear enough signal to investigate white dwarf interiors through
gravitational wave asteroseismology.Comment: Accepted for Astrophysical Journal Letters. Changed value of
branching ratio resulting in an order of magnitude drop in gravitational wave
amplitude
A How-To for the Mock LISA Data Challenges
The LISA International Science Team Working Group on Data Analysis
(LIST-WG1B) is sponsoring several rounds of mock data challenges, with the
purpose of fostering development of LISA data-analysis capabilities, and of
demonstrating technical readiness for the maximum science exploitation of the
LISA data. The first round of challenge data sets were released at this
Symposium. We describe the models and conventions (for LISA and for
gravitational-wave sources) used to prepare the data sets, the file format used
to encode them, and the tools and resources available to support challenge
participants.Comment: 10 pages, 1 figure, in Proceedings of the Sixth International LISA
Symposium (AIP, 2006
Inspiralling compact binaries in quasi-elliptical orbits: The complete third post-Newtonian energy flux
The instantaneous contributions to the 3PN gravitational wave luminosity from
the inspiral phase of a binary system of compact objects moving in a quasi
elliptical orbit is computed using the multipolar post-Minkowskian wave
generation formalism. The necessary inputs for this calculation include the 3PN
accurate mass quadrupole moment for general orbits and the mass octupole and
current quadrupole moments at 2PN. Using the recently obtained 3PN
quasi-Keplerian representation of elliptical orbits the flux is averaged over
the binary's orbit. Supplementing this by the important hereditary
contributions arising from tails, tails-of-tails and tails squared terms
calculated in a previous paper, the complete 3PN energy flux is obtained. The
final result presented in this paper would be needed for the construction of
ready-to-use templates for binaries moving on non-circular orbits, a plausible
class of sources not only for the space based detectors like LISA but also for
the ground based ones.Comment: 40 pages. Minor changes in text throughout. Minor typos in Eqs.
(3.3b), (7.7f), (8.19d) and (8.20) corrected. Matches the published versio
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