6,019 research outputs found
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
Estimating tropical forest biomass with a combination of SAR image texture and Landsat TM data:an assessment of predictions between regions
LISA Response Function and Parameter Estimation
We investigate the response function of LISA and consider the adequacy of its
commonly used approximation in the high-frequency range of the observational
band. We concentrate on monochromatic binary systems, such as white dwarf
binaries. We find that above a few mHz the approxmation starts becoming
increasingly inaccurate. The transfer function introduces additional amplitude
and phase modulations in the measured signal that influence parameter estmation
and, if not properly accounted for, lead to losses of signal-to-noise ratio.Comment: 4 pages, 2 figures, amaldi 5 conference proceeding
LISA data analysis: The monochromatic binary detection and initial guess problems
We consider the detection and initial guess problems for the LISA
gravitational wave detector. The detection problem is the problem of how to
determine if there is a signal present in instrumental data and how to identify
it. Because of the Doppler and plane-precession spreading of the spectral power
of the LISA signal, the usual power spectrum approach to detection will have
difficulty identifying sources. A better method must be found. The initial
guess problem involves how to generate {\it a priori} values for the parameters
of a parameter-estimation problem that are close enough to the final values for
a linear least-squares estimator to converge to the correct result. A useful
approach to simultaneously solving the detection and initial guess problems for
LISA is to divide the sky into many pixels and to demodulate the Doppler
spreading for each set of pixel coordinates. The demodulated power spectra may
then be searched for spectral features. We demonstrate that the procedure works
well as a first step in the search for gravitational waves from monochromatic
binaries.Comment: 8 pages, 8 figure
Detection of high energy X-rays from the galactic center region
Observations of the galactic center region made with the high energy X-ray detector on OSO-8 are discussed. A strong hard X-ray which was detected during these observations from the vicinity of the galactic center are examined. The counting rate spectrum and the photon number spectrum of the flux are determined. Comparisons with the high energy X-ray fluxes observed from sources in the region by others are discussed
LISA, binary stars, and the mass of the graviton
We extend and improve earlier estimates of the ability of the proposed LISA
(Laser Interferometer Space Antenna) gravitational wave detector to place upper
bounds on the graviton mass, m_g, by comparing the arrival times of
gravitational and electromagnetic signals from binary star systems. We show
that the best possible limit on m_g obtainable this way is ~ 50 times better
than the current limit set by Solar System measurements. Among currently known,
well-understood binaries, 4U1820-30 is the best for this purpose; LISA
observations of 4U1820-30 should yield a limit ~ 3-4 times better than the
present Solar System bound. AM CVn-type binaries offer the prospect of
improving the limit by a factor of 10, if such systems can be better understood
by the time of the LISA mission. We briefly discuss the likelihood that radio
and optical searches during the next decade will yield binaries that more
closely approach the best possible case.Comment: ReVTeX 4, 6 pages, 1 figure, submitted to Phys Rev
The high-energy pulsed X-ray spectrum of HER X-1 as observed with OSO-8
Her X-1 was observed from 1977 August 30 to September 10 using the High-Energy X-Ray Scintillation Spectrometer on board the OSO-8 satellite. The observation, during which the source was monitored continually for nearly an entire ON-state, covered the energy range from 16 to 280 keV. Pulsed flux measurements as a function of binary orbit and binary phase are presented for energies between 16 and 98 keV. The pulsed flux between 16 and 33 keV exhibited a sharp decrease following the fourth binary orbit and was consistent with zero pulsed flux thereafter. The pulsed spectrum was fitted with a power law, a thermal spectrum without features, and a thermal spectrum with a superposed gaussian centered at 55 keV. The latter fit has the smallest value of chi - squared per degree of freedom, and the resulting integrated line intensity is 1.5 superscript + 4.1 subscript - 1.4 x .001 photons s superscript-1 cm superscript-2 for a width of 3.1 superscript + 9.1 subscript -2.6 keV. This result, while of low statistical significance, agrees with the value observed by Trumper (1978) during the same On-state
Estimating the detectable rate of capture of stellar mass black holes by massive central black holes in normal galaxies
The capture and subsequent inspiral of stellar mass black holes on eccentric
orbits by central massive black holes, is one of the more interesting likely
sources of gravitational radiation detectable by LISA. We estimate the rate of
observable events and the associated uncertainties. A moderately favourable
mass function could provide many detectable bursts each year, and a detection
of at least one burst per year is very likely given our current understanding
of the populations in cores of normal spiral galaxies.Comment: 3 pages 2-column revtex Latex macro. No figures. Classical and
Quantum Gravity, accepte
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
Annual modulation of the Galactic binary confusion noise bakground and LISA data analysis
We study the anisotropies of the Galactic confusion noise background and its
effects on LISA data analysis. LISA has two data streams of the gravitational
waves signals relevant for low frequency regime. Due to the anisotropies of the
background, the matrix for their confusion noises has off-diagonal components
and depends strongly on the orientation of the detector plane. We find that the
sky-averaged confusion noise level could change by a factor of 2
in three months, and would be minimum when the orbital position of LISA is
either around the spring or autumn equinox.Comment: 13 pages, 6 figure
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