183 research outputs found
Gravitational Radiation from Black Hole Binaries in Globular Clusters
A populations of stellar mass black hole binaries may exist in globular
clusters. The dynamics of globular cluster evolution imply that there may be at
most one black hole binary is a globular cluster. The population of binaries
are expected to have orbital periods greater than a few hours and to have a
thermal distribution of eccentricities. In the LISA band, the gravitational
wave signal from these binaries will consist of several of the higher harmonics
of the orbital frequency. A Monte Carlo simulation of the galactic globular
cluster system indicates that LISA will detect binaries in 10 % of the clusters
with an angular resolution sufficient to identify the host cluster of the
binary.Comment: 7 pages, 2 eps figures, uses iopart styl
Compact Binaries in Star Clusters II - Escapers and Detection Rates
We use a self-consistent Monte Carlo treatment of stellar dynamics to
investigate black hole binaries that are dynamically ejected from globular
clusters to determine if they will be gravitational wave sources. We find that
many of the ejected binaries have initially short periods and will merge within
a Hubble time due to gravitational wave radiation. Thus they are potential
sources for ground-based gravitational wave detectors. We estimate the yearly
detection rate for current and advanced ground-based detectors and find a
modest enhancement over the rate predicted for binaries produced by pure
stellar evolution in galactic fields. We also find that many of the ejected
binaries will pass through the longer wavelength Laser Interferometer Space
Antenna (LISA) band and may be individually resolvable. We find a low
probability that the Galaxy will contain a binary in the LISA band during its
three-year mission. Some such binaries may, however, be detectable at Mpc
distances implying that there may be resolvable stellar-mass LISA sources
beyond our Galaxy. We conclude that globular clusters have a significant effect
on the detection rate of ground-based detectors and may produce interesting
LISA sources in local group galaxies.Comment: 19 pages, 16 figures, 2 tables, submitted to MNRA
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
A Simulation of the LISA Data Stream from Galactic White Dwarf Binaries
Gravitational radiation from the galactic population of white dwarf binaries
is expected to produce a background signal in the LISA frequency band. At
frequencies below 1 mHz, this signal is expected to be confusion-limited and
has been approximated as gaussian noise. At frequencies above about 5 mHz, the
signal will consist of separable individual sources. We have produced a
simulation of the LISA data stream from a population of 90k galactic binaries
in the frequency range between 1 - 5 mHz. This signal is compared with the
simulated signal from globular cluster populations of binaries. Notable
features of the simulation as well as potential data analysis schemes for
extracting information are presented.Comment: Submitted to QC
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
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
Report on the second Mock LISA Data Challenge
The Mock LISA Data Challenges are a program to demonstrate LISA data-analysis capabilities and to encourage their development. Each round of challenges consists of several data sets containing simulated instrument noise and gravitational-wave sources of undisclosed parameters. Participants are asked to analyze the data sets and report the maximum information about source parameters. The challenges are being released in rounds of increasing complexity and realism: in this proceeding we present the results of Challenge 2, issued in January 2007, which successfully demonstrated the recovery of signals from supermassive black-hole binaries, from ~20,000 overlapping Galactic white-dwarf binaries, and from the extreme-mass-ratio inspirals of compact objects into central galactic black holes
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
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
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
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