998 research outputs found
Elimination of Clock Jitter Noise in Spaceborn Laser Interferometers
Space gravitational wave detectors employing laser interferometry between
free-flying spacecraft differ in many ways from their laboratory counterparts.
Among these differences is the fact that, in space, the end-masses will be
moving relative to each other. This creates a problem by inducing a Doppler
shift between the incoming and outgoing frequencies. The resulting beat
frequency is so high that its phase cannot be read to sufficient accuracy when
referenced to state-of-the-art space-qualified clocks. This is the problem that
is addressed in this paper. We introduce a set of time-domain algorithms in
which the effects of clock jitter are exactly canceled. The method employs the
two-color laser approach that has been previously proposed, but avoids the
singularities that arise in the previous frequency-domain algorithms. In
addition, several practical aspects of the laser and clock noise cancellation
schemes are addressed.Comment: 20 pages, 5 figure
The Effects of Orbital Motion on LISA Time Delay Interferometry
In an effort to eliminate laser phase noise in laser interferometer
spaceborne gravitational wave detectors, several combinations of signals have
been found that allow the laser noise to be canceled out while gravitational
wave signals remain. This process is called time delay interferometry (TDI). In
the papers that defined the TDI variables, their performance was evaluated in
the limit that the gravitational wave detector is fixed in space. However, the
performance depends on certain symmetries in the armlengths that are available
if the detector is fixed in space, but that will be broken in the actual
rotating and flexing configuration produced by the LISA orbits. In this paper
we investigate the performance of these TDI variables for the real LISA orbits.
First, addressing the effects of rotation, we verify Daniel Shaddock's result
that the Sagnac variables will not cancel out the laser phase noise, and we
also find the same result for the symmetric Sagnac variable. The loss of the
latter variable would be particularly unfortunate since this variable also
cancels out gravitational wave signal, allowing instrument noise in the
detector to be isolated and measured. Fortunately, we have found a set of more
complicated TDI variables, which we call Delta-Sagnac variables, one of which
accomplishes the same goal as the symmetric Sagnac variable to good accuracy.
Finally, however, as we investigate the effects of the flexing of the detector
arms due to non-circular orbital motion, we show that all variables, including
the interferometer variables, which survive the rotation-induced loss of
direction symmetry, will not completely cancel laser phase noise when the
armlengths are changing with time. This unavoidable problem will place a
stringent requirement on laser stability of 5 Hz per root Hz.Comment: 12 pages, 2 figure
Data Processing for LISA's Laser Interferometer Tracking System (LITS)
The purpose of this paper is twofold. First, we will present recent results
on the data processing for LISA, including algorithms for elimination of clock
jitter noise and discussion of the generation of the data averages that will
eventually need to be telemetered to the ground. Second, we will argue, based
partly on these results, that a laser interferometer tracking system (LITS)
that employs independent lasers in each spacecraft is preferable for reasons of
simplicity to that in which the lasers in two of the spacecraft are locked to
the incoming beam from the third.Comment: 5 pages, Proceedings of the Third LISA Symposium (Golm, Germany,
2000
The information content of gravitational wave harmonics in compact binary inspiral
The nonlinear aspect of gravitational wave generation that produces power at
harmonics of the orbital frequency, above the fundamental quadrupole frequency,
is examined to see what information about the source is contained in these
higher harmonics. We use an order (4/2) post-Newtonian expansion of the
gravitational wave waveform of a binary system to model the signal seen in a
spaceborne gravitational wave detector such as the proposed LISA detector.
Covariance studies are then performed to determine the ultimate accuracy to be
expected when the parameters of the source are fit to the received signal. We
find three areas where the higher harmonics contribute crucial information that
breaks degeneracies in the model and allows otherwise badly-correlated
parameters to be separated and determined. First, we find that the position of
a coalescing massive black hole binary in an ecliptic plane detector, such as
OMEGA, is well-determined with the help of these harmonics. Second, we find
that the individual masses of the stars in a chirping neutron star binary can
be separated because of the mass dependence of the harmonic contributions to
the wave. Finally, we note that supermassive black hole binaries, whose
frequencies are too low to be seen in the detector sensitivity window for long,
may still have their masses, distances, and positions determined since the
information content of the higher harmonics compensates for the information
lost when the orbit-induced modulation of the signal does not last long enough
to be apparent in the data.Comment: 13 pages, 5 figure
Sensitivity curves for spaceborne gravitational wave interferometers
To determine whether particular sources of gravitational radiation will be
detectable by a specific gravitational wave detector, it is necessary to know
the sensitivity limits of the instrument. These instrumental sensitivities are
often depicted (after averaging over source position and polarization) by
graphing the minimal values of the gravitational wave amplitude detectable by
the instrument versus the frequency of the gravitational wave. This paper
describes in detail how to compute such a sensitivity curve given a set of
specifications for a spaceborne laser interferometer gravitational wave
observatory. Minor errors in the prior literature are corrected, and the first
(mostly) analytic calculation of the gravitational wave transfer function is
presented. Example sensitivity curve calculations are presented for the
proposed LISA interferometer. We find that previous treatments of LISA have
underestimated its sensitivity by a factor of .Comment: 27 pages + 5 figures, REVTeX, accepted for publication in Phys Rev D;
Update reflects referees comments, figure 3 clarified, figure 5 corrected for
LISA baselin
LATOR Covariance Analysis
We present results from a covariance study for the proposed Laser Astrometric
Test of Relativity (LATOR) mission. This mission would send two
laser-transmitter spacecraft behind the Sun and measure the relative
gravitational light bending of their signals using a hundred-meter-baseline
optical interferometer to be constructed on the International Space Station. We
assume that each spacecraft is equipped with a drag-free system and assume
approximately one year of data. We conclude that the observations allow a
simultaneous determination of the orbit parameters of the spacecraft and of the
Parametrized Post-Newtonian (PPN) parameter with an uncertainty of
. We also find a determination of the
solar quadrupole moment, , as well as the first measurement of the
second-order post-PPN parameter to an accuracy of about .Comment: 9 pages, 3 figures. first revision: minor changes to results. Second
revision: additional discussion of orbit modelling and LATOR drag-free system
requirement feasibility. Added references to tables I and V (which list PPN
parameter uncertainties), removed word from sentence in Section III. 3rd
revision: removed 2 incorrect text fragments (referring to impact parameter
as distance of closest approach) and reference to upcoming publication of
ref. 2, removed spurious gamma from eq. 1 - Last error is still in cqg
published versio
LISA data analysis I: Doppler demodulation
The orbital motion of the Laser Interferometer Space Antenna (LISA) produces
amplitude, phase and frequency modulation of a gravitational wave signal. The
modulations have the effect of spreading a monochromatic gravitational wave
signal across a range of frequencies. The modulations encode useful information
about the source location and orientation, but they also have the deleterious
affect of spreading a signal across a wide bandwidth, thereby reducing the
strength of the signal relative to the instrument noise. We describe a simple
method for removing the dominant, Doppler, component of the signal modulation.
The demodulation reassembles the power from a monochromatic source into a
narrow spike, and provides a quick way to determine the sky locations and
frequencies of the brightest gravitational wave sources.Comment: 5 pages, 7 figures. References and new comments adde
In-line UV spectroscopy for the quantification of low-dose active ingredients during the manufacturing of pharmaceutical semi-solid and liquid formulations
Static post-Newtonian equivalence of GR and gravity with a dynamical preferred frame
A generally covariant extension of general relativity (GR) in which a
dynamical unit timelike vector field is coupled to the metric is studied in the
asymptotic weak field limit of spherically symmetric static solutions. The two
post-Newtonian parameters known as the Eddington-Robertson-Schiff parameters
are found to be identical to those in the case of pure GR, except for some
non-generic values of the coefficients in the Lagrangian.Comment: 13 pages; v.2: minor editing, signs corrected, version to appear in
PRD; v. 3: signs corrected in eqn (3
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