141 research outputs found
Simulation of the White Dwarf -- White Dwarf galactic background in the LISA data
LISA (Laser Interferometer Space Antenna) is a proposed space mission, which
will use coherent laser beams exchanged between three remote spacecraft to
detect and study low-frequency cosmic gravitational radiation. In the low-part
of its frequency band, the LISA strain sensitivity will be dominated by the
incoherent superposition of hundreds of millions of gravitational wave signals
radiated by inspiraling white-dwarf binaries present in our own galaxy. In
order to estimate the magnitude of the LISA response to this background, we
have simulated a synthesized population that recently appeared in the
literature. We find the amplitude of the galactic white-dwarf binary background
in the LISA data to be modulated in time, reaching a minimum equal to about
twice that of the LISA noise for a period of about two months around the time
when the Sun-LISA direction is roughly oriented towards the Autumn equinox.
Since the galactic white-dwarfs background will be observed by LISA not as a
stationary but rather as a cyclostationary random process with a period of one
year, we summarize the theory of cyclostationary random processes and present
the corresponding generalized spectral method needed to characterize such
process. We find that, by measuring the generalized spectral components of the
white-dwarf background, LISA will be able to infer properties of the
distribution of the white-dwarfs binary systems present in our Galaxy.Comment: 14 pages and 6 figures. Submitted to Classical and Quantum Gravity
(Proceedings of GWDAW9
Progress in Interferometry for LISA at JPL
Recent advances at JPL in experimentation and design for LISA interferometry
include the demonstration of Time Delay Interferometry using electronically
separated end stations, a new arm-locking design with improved gain and
stability, and progress in flight readiness of digital and analog electronics
for phase measurements.Comment: 11 pages, 9 figures, LISA 8 Symposium, Stanford University, 201
A hierarchical search for gravitational waves from supermassive black hole binary mergers
We present a method to search for gravitational waves from coalescing
supermassive binary black holes in LISA data. The search utilizes the
-statistic to maximize over, and determine the values of, the
extrinsic parameters of the binary system. The intrinsic parameters are
searched over hierarchically using stochastically generated multi-dimensional
template banks to recover the masses and sky locations of the binary. We
present the results of this method applied to the mock LISA data Challenge 1B
data set.Comment: 11 pages, 2 figures, for GWDAW-12 proceedings edition of CQ
Modulation of LISA free-fall orbits due to the Earth-Moon system
We calculate the effect of the Earth-Moon (EM) system on the free-fall motion
of LISA test masses. We show that the periodic gravitational pulling of the EM
system induces a resonance with fundamental frequency 1 yr^-1 and a series of
periodic perturbations with frequencies equal to integer harmonics of the
synodic month (9.92 10^-7 Hz). We then evaluate the effects of these
perturbations (up to the 6th harmonics) on the relative motions between each
test masses couple, finding that they range between 3mm and 10pm for the 2nd
and 6th harmonic, respectively. If we take the LISA sensitivity curve, as
extrapolated down to 10^-6 Hz, we obtain that a few harmonics of the EM system
can be detected in the Doppler data collected by the LISA space mission. This
suggests that the EM system gravitational near field could provide an absolute
calibration for the LISA sensitivity at very low frequencies.Comment: 15 pages, 5 figure
Numerical simulation of time delay interferometry for eLISA/NGO
eLISA/NGO is a new gravitational wave detection proposal with arm length of
10^6 km and one interferometer down-scaled from LISA. Just like LISA and
ASTROD-GW, in order to attain the requisite sensitivity for eLISA/NGO, laser
frequency noise must be suppressed to below the secondary noises such as the
optical path noise, acceleration noise etc. In previous papers, we have
performed the numerical simulation of the time delay interferometry (TDI) for
LISA and ASTROD-GW with one arm dysfunctional by using the CGC 2.7 ephemeris.
The results are well below their respective limits which the laser frequency
noise is required to be suppressed. In this paper, we follow the same procedure
to simulate the time delay interferometry numerically. To do this, we work out
a set of 1000-day optimized mission orbits of the eLISA/NGO spacecraft starting
at January 1st, 2021 using the CGC 2.7 ephemeris framework. We then use the
numerical method to calculate the residual optical path differences in the
second-generation TDI solutions as in our previous papers. The maximum path
length difference, for all configurations calculated, is below 13 mm (43 ps).
It is well below the limit which the laser frequency noise is required to be
suppressed for eLISA/NGO. We compare and discuss the resulting differences due
to the different arm lengths for various mission proposals -- eLISA/NGO, an
NGO-LISA-type mission with a nominal arm length of 2 x 10^6 km, LISA and
ASTROD-GW.Comment: 17 pages, 13 figures, 3 tables, minor changes in description to match
the accepted version of Classical and Quantum Gravity. arXiv admin note: text
overlap with arXiv:1102.496
A Three-Stage Search for Supermassive Black Hole Binaries in LISA Data
Gravitational waves from the inspiral and coalescence of supermassive
black-hole (SMBH) binaries with masses ~10^6 Msun are likely to be among the
strongest sources for the Laser Interferometer Space Antenna (LISA). We
describe a three-stage data-analysis pipeline designed to search for and
measure the parameters of SMBH binaries in LISA data. The first stage uses a
time-frequency track-search method to search for inspiral signals and provide a
coarse estimate of the black-hole masses m_1, m_2 and of the coalescence time
of the binary t_c. The second stage uses a sequence of matched-filter template
banks, seeded by the first stage, to improve the measurement accuracy of the
masses and coalescence time. Finally, a Markov Chain Monte Carlo search is used
to estimate all nine physical parameters of the binary. Using results from the
second stage substantially shortens the Markov Chain burn-in time and allows us
to determine the number of SMBH-binary signals in the data before starting
parameter estimation. We demonstrate our analysis pipeline using simulated data
from the first LISA Mock Data Challenge. We discuss our plan for improving this
pipeline and the challenges that will be faced in real LISA data analysis.Comment: 12 pages, 3 figures, submitted to Proceedings of GWDAW-11 (Berlin,
Dec. '06
Orbital effects of a monochromatic plane gravitational wave with ultra-low frequency incident on a gravitationally bound two-body system
We analytically compute the long-term orbital variations of a test particle
orbiting a central body acted upon by an incident monochromatic plane
gravitational wave. We assume that the characteristic size of the perturbed
two-body system is much smaller than the wavelength of the wave. Moreover, we
also suppose that the wave's frequency is much smaller than the particle's
orbital one. We make neither a priori assumptions about the direction of the
wavevector nor on the orbital geometry of the planet. We find that, while the
semi-major axis is left unaffected, the eccentricity, the inclination, the
longitude of the ascending node, the longitude of pericenter and the mean
anomaly undergo non-vanishing long-term changes. They are not secular trends
because of the slow modulation introduced by the tidal matrix coefficients and
by the orbital elements themselves. They could be useful to indepenedently
constrain the ultra-low frequency waves which may have been indirectly detected
in the BICEP2 experiment. Our calculation holds, in general, for any
gravitationally bound two-body system whose characteristic frequency is much
larger than the frequency of the external wave. It is also valid for a generic
perturbation of tidal type with constant coefficients over timescales of the
order of the orbital period of the perturbed particle.Comment: LaTex2e, 24 pages, no figures, no tables. Changes suggested by the
referees include
A qualitative evaluation of a novel intervention using insight into tobacco industry tactics to prevent the uptake of smoking in school-aged children
Background: Evidence from the US Truth campaign suggests that interventions focusing on tobacco industry tactics can be effective in preventing smoking uptake by children. Operation Smoke Storm is the first school-based intervention based on this premise and comprises three classroom sessions in which students act as secret agents uncovering tobacco industry tactics through videos, quizzes, discussions, and presentations. We report a qualitative evaluation of its acceptability.
Methods: We conducted eight focus groups with 79 students aged 11-12 who participated in Operation Smoke Storm at two UK schools in Autumn 2013, and 20 interviews with teachers who delivered the intervention. These were digitally audio-recorded, transcribed verbatim and analysed using the framework method.
Results: Students enjoyed the secret agent scenario and reported acquiring new knowledge about smoking and the tobacco industry, which seemed to strengthen their aversion to smoking. Teachers felt confident delivering the ‘off the shelf’ resource, although they would have welcomed more background information about the topic and guidance on steering discussions. Teachers highlighted a need for the resource to be flexible and not dependent on lesson length, teacher confidence, or expertise. Students and teachers endorsed the idea of developing a booster component for older students and supported the development of printed information complementing the resource to encourage parents to support their child not to smoke.
Conclusions: These findings demonstrate that Operation Smoke Storm can be delivered by teachers to raise awareness about smoking-related issues. The ideas and issues raised are now being used to improve and extend the resource for further evaluation
Fundamentals of the LISA Stable Flight Formation
The joint NASA-ESA mission LISA relies crucially on the stability of the
three spacecraft constellation. Each of the spacecraft is in heliocentric
orbits forming a stable triangle. The principles of such a formation flight
have been formulated long ago and analysis performed, but seldom presented if
ever, even to LISA scientists. We nevertheless need these details in order to
carry out theoretical studies on the optical links, simulators etc. In this
article, we present in brief, a model of the LISA constellation, which we
believe will be useful for the LISA community.Comment: 9 Pages, 2 Figure Submitted to Classical and Quantum Gravit
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