118879701
Tuning gravitational-wave detector networks to measure compact binary mergers
Gravitational waves generated by the final merger of compact binary systems depend on the structure of the binary's members. If the binary contains neutron stars, measuring such waves can teach us about the properties of matter at extreme densities. Unfortunately, these waves are typically at high frequency where the sensitivity of broadband detectors is not good. Learning about dense matter from these waves will require networks of broadband detectors combined with narrowband detectors that have good sensitivity at high frequencies. This paper presents an algorithm by which a network can be ``tuned,'' in accordance with the best available information, in order to most effectively measure merger waves. The algorithm is presented in the context of a toy model that captures the qualitative features of narrowband detectors and of certain binary neutron star merger wave models. By using what is learned from a sequence of merger measurements, the network can be gradually tuned in order to accurately measure the waves. The number of measurements needed to reach this stage depends upon the waves' signal strength, the number of narrowband detectors available for the measurement, and the detailed characteristics of the waves that carry the merger information. Future studies will go beyond this toy model, encompassing a more realistic description of both the detectors and the gravitational waves.
8108905
Untangling the merger history of massive black holes with LISA
Binary black hole coalescences emit gravitational waves that will be measurable by the space-based detector LISA to large redshifts. This suggests that LISA may be able to observe black holes grow and evolve as the Universe evolves, mapping the distribution of black hole masses as a function of redshift. An immediate difficulty with this idea is that LISA measures certain redshifted combinations of masses with good accuracy: if a system has some mass parameter m, then LISA measures (1 + z)m. This mass-redshift degeneracy makes it difficult to follow the mass evolution. In many cases, LISA will also measure the luminosity distance D of a coalescence accurately. Since cosmological parameters (particularly the mean density, the cosmological constant and the Hubble constant) are now known with moderate precision, we can obtain z from D and break the degeneracy. This makes it possible to untangle the mass and redshift and to study the mass and merger history of black holes. Mapping the black hole mass distribution could open a window on to an early epoch of structure formation.
16126239
Seismic gravity-gradient noise in interferometric gravitational-wave detectors
When ambient seismic waves pass near and under an interferometric gravitational-wave detector, they induce density perturbations in the earth, which in turn produce fluctuating gravitational forces on the interferometer’s test masses. These forces mimic a stochastic background of gravitational waves and thus constitute a noise source. This seismic gravitygradient noise has been estimated and discussed previously by Saulson using a simple model of the earth’s ambient seismic motions. In this paper, we develop a more sophisticated model of these motions, based on the theory of multimode Rayleigh and Love waves propagating in a multilayer medium that approximates the geological strata at the LIGO sites (Tables II–IV), and we use this model to revisit seismic gravity gradients. We characterize the seismic gravity-gradient noise by a transfer function, T (f) ≡ x̃(f)/W̃ (f), from the spectrum of rms seismic displacements averaged over vertical and horizontal directions, W̃ (f), to the spectrum of interferometric test-mass motions, x̃(f) ≡ Lh̃(f); here L is the interferometer arm length, h̃(f) is the gravitational-wave noise spectrum, and f is frequency. Our model predicts a transfer function with essentially the same functional form as that derived by Saulson, T ' 4πGρ(2πf)β(f), where ρ is the density of the earth near the test masses, G is Newton’s constant, and β(f) ≡ γ(f)Γ(f)β(f) is a dimensionless reduced transfer function whose components γ ' 1 and Γ ' 1 account for a weak correlation between the interferometer’s two test masses (Fig. 1) and a slight reduction of the noise due to the height of the test masses above the earth’s surface. This paper’s primary foci are (i) a study of how β(f) ' β(f) depends on the various Rayleigh and Love modes that are present in the seismic spectrum (Figs. 4–11 and Table I), (ii) an attempt to estimate which modes are actually present at the two LIGO sites at quiet times and at noisy times, and (iii) a corresponding estimate of the magnitude of β(f) at quiet and noisy times. We conclude that at quiet times β ' 0.35–0.6 at the LIGO sites, and at noisy times β ' 0.15–1.4. (For comparison, Saulson’s simple model gave β = β = 1/ √ 3 = 0.58.) By folding our resulting transfer function into the “standard LIGO seismic spectrum” [Eq. (1.29)], which approximates W̃ (f) at typical times, we obtain the gravity-gradient noise spectra shown in Fig. 2. At quiet times this noise is below the benchmark noise level of “advanced LIGO interferometers” at all frequencies (though not by much at ∼ 10 Hz); at noisy times it may significantly exceed the advanced noise level near 10 Hz. The lower edge of our quiet-time noise constitutes a limit, beyond which there would be little gain from further improvements in vibration isolation and thermal noise, unless one can also reduce the seismic gravity gradient noise. Two methods of such reduction are briefly discussed: monitoring the earth’s density perturbations near each test mass, computing the gravitational forces they produce, and correcting the data for those forces; and constructing narrow moats around the interferometers’ corner and end stations to shield out the fundamental-mode Rayleigh waves, which we suspect dominate at quiet times.
119020610
Towards adiabatic waveforms for inspiral into Kerr black holes : A new model of the source for the time domain perturbation equation
We revisit the problem of the emission of gravitational waves from a test mass orbiting and thus perturbing a Kerr black hole. The source term of the Teukolsky perturbation equation contains a Dirac delta function which represents a point particle. We present a technique to effectively model the delta function and its derivatives using as few as four points on a numerical grid. The source term is then incorporated into a code that evolves the Teukolsky equation in the time domain as a (2+1) dimensional partial differential equation. The waveforms and energy fluxes are extracted far from the black hole. Our comparisons with earlier work show an order of magnitude gain in performance (speed) and numerical errors less than 1% for a large fraction of parameter space. As a first application of this code, we analyze the effect of finite extraction radius on the energy fluxes. This paper is the first in a series whose goal is to develop adiabatic waveforms describing the inspiral of a small compact body into a massive Kerr black hole.
1891241
How black holes get their kicks: Radiation recoil in binary black hole mergers
Gravitational waves from the coalescence of binary black holes carry linear momentum, causing center of mass recoil. This ``radiation rocket'' has important implications for systems with escape speeds of order the recoil velocity. We describe new recoil calculations using high precision black hole perturbation theory to estimate the magnitude of the recoil for the slow ``inspiral'' coalescence phase; coupled with a cruder calculation for the final ``plunge'', we estimate the total recoil imparted to a merged black hole. We find that velocities of many tens to a few hundred km/sec can be achieved fairly easily. The recoil probably never exceeds about 500 km/sec.
36773341
Circular and non-circular nearly horizon-skimming orbits in Kerr spacetimes
We have performed a detailed analysis of orbital motion in the vicinity of a nearly extremal Kerr black hole. For very rapidly rotating black holes—spin parameter aJ=M > 0:9524M —we have found a class of very strong-field eccentric orbits whose orbital angular momentum Lz increases with the orbit's inclination with respect to the equatorial plane, while keeping latus rectum and eccentricity fixed. This behavior is in contrast with Newtonian intuition, and is in fact opposite to the normal behavior of black hole orbits. Such behavior was noted previously for circular orbits; since it only applies to orbits very close to the black hole, they were named ''nearly horizon-skimming orbits.'' Our current analysis generalizes this result, mapping out the full generic (inclined and eccentric) family of nearly horizon- skimming orbits. The earlier work on circular orbits reported that, under gravitational radiation emission, nearly horizon-skimming orbits exhibit unusual inspiral, tending to evolve to smaller orbit inclination, toward prograde equatorial configuration. Normal orbits, by contrast, always demonstrate slowly growing orbit inclination —orbits evolve toward the retrograde equatorial configuration. Using up-to-date Teukolsky-based fluxes, we have concluded that the earlier result was incorrect —all circular orbits, including nearly horizon-skimming ones, exhibit growing orbit inclination under radiative backreaction. Using kludge fluxes based on a Post-Newtonian expansion corrected with fits to circular and to equatorial Teukolsky-based fluxes, we argue that the inclination grows also for eccentric nearly horizon-skimming orbits. We also find that the inclination change is, in any case, very small. As such, we conclude that these orbits are not likely to have a clear and peculiar imprint on the gravitational waveforms expected to be measured by the space-based detector LISA.
121262274
The Whipple Observatory 10 m gamma-ray telescope, 1997–2006
Abstract Details are presented of the Whipple Observatory’s 10 m atmospheric Cherenkov telescope and camera, as it evolved during the period 1997 until 2006. The design of the telescope and camera’s optical and electronic systems is discussed together with a detailed description of the four-stage GRANITE (Gamma-RAy New Imaging TElescope) upgrade program, undertaken during the same time period. The objective of the upgrade was to improve the telescope’s sensitivity for the detection of very-high-energy gamma-rays. Results from the program are provided and are briefly discussed in the context of the design of VERITAS.
119858324
Anyons from bosons
Abstract We consider systems containing two or more distinct species of particles in two spatial dimensions. In quantizations of these systems, the statistics of composites containing more than one type of particle are not completely determined by the statistics of the constituents. In particular there exist quantum theories in which two bosons can combine to form an anyon with any desired statistical angle. We demonstrate these results using the topological approach to quantum kinematics, which in this case leads to a generalization of ordinary braid theory in two dimensions. Comparisons are made to three-dimensional systems.
119097691
Final Results from the Hubble Space Telescope Key Project to Measure the Hubble Constant
We present here the final results of the Hubble Space Telescope (HST) Key Project to measure the Hubble constant. We summarize our method, the results, and the uncertainties, tabulate our revised distances, and give the implications of these results for cosmology. Our results are based on a Cepheid calibration of several secondary distance methods applied over the range of about 60-400 Mpc. The analysis presented here benefits from a number of recent improvements and refinements, including (1) a larger LMC Cepheid sample to define the fiducial period-luminosity (PL) relations, (2) a more recent HST Wide Field and Planetary Camera 2 (WFPC2) photometric calibration, (3) a correction for Cepheid metallicity, and (4) a correction for incompleteness bias in the observed Cepheid PL samples. We adopt a distance modulus to the LMC (relative to which the more distant galaxies are measured) of μ0 = 18.50 ± 0.10 mag, or 50 kpc. New, revised distances are given for the 18 spiral galaxies for which Cepheids have been discovered as part of the Key Project, as well as for 13 additional galaxies with published Cepheid data. The new calibration results in a Cepheid distance to NGC 4258 in better agreement with the maser distance to this galaxy. Based on these revised Cepheid distances, we find values (in km s-1 Mpc-1) of H0 = 71 ± 2 ± 6 (systematic) (Type Ia supernovae), H0 = 71 ± 3 ± 7 (Tully-Fisher relation), H0 = 70 ± 5 ± 6 (surface brightness fluctuations), H0 = 72 ± 9 ± 7 (Type II supernovae), and H0 = 82 ± 6 ± 9 (fundamental plane). We combine these results for the different methods with three different weighting schemes, and find good agreement and consistency with H0 = 72 ± 8 km s-1 Mpc-1. Finally, we compare these results with other, global methods for measuring H0.
197531313
The HST Key Project on the Extragalactic Distance Scale. XXVIII. Combining the Constraints on the Hubble Constant
Since the launch of the Hubble Space Telescope nine years ago, Cepheid distances to 25 galaxies have been determined for the purpose of calibrating secondary distance indicators. A variety of these can now be calibrated, and the accompanying papers by Sakai, Kelson, Ferrarese, and Gibson employ the full set of 25 galaxies to consider the Tully-Fisher relation, the fundamental plane of elliptical galaxies, Type Ia supernovae, and surface brightness fluctuations. 
When calibrated with Cepheid distances, each of these methods yields a measurement of the Hubble constant and a corresponding measurement uncertainty. We combine these measurements in this paper, together with a model of the velocity field, to yield the best available estimate of the value of H_0 within the range of these secondary distance indicators and its uncertainty. 
The result is H_0 = 71 +/- 6 km/sec/Mpc. The largest contributor to the uncertainty of this 67% confidence level result is the distance of the Large Magellanic Cloud, which has been assumed to be 50 +/- 3 kpc.
119352682
The Extragalactic Distance Scale Key Project. XVIII. The Discovery of Cepheids and a New Distance to NGC 4535 Using the Hubble Space Telescope
We report on the discovery of Cepheids in the Virgo spiral galaxy NGC 4535, based on observations made with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope (HST). NGC 4535 is one of 18 galaxies observed as a part of The HST Key Project on the Extragalactic Distance Scale, which aims to measure the Hubble constant to 10% accuracy. NGC 4535 was observed over 13 epochs using the F555W filter, and over 9 epochs using the F814W filter. The HST F555W and F814W data were transformed to the Johnson V and Kron-Cousins I magnitude systems, respectively. Photometry was performed using two independent programs, DoPHOT and DAOPHOT II/ALLFRAME. Period-luminosity relations in the V and I bands were constructed using 39 high-quality Cepheids present in our set of 50 variable candidates. We obtain a distance modulus of 31.02 ± 0.26 mag, corresponding to a distance of 16.0 ± 1.9 Mpc. Our distance estimate is based on values of μ0 = 18.50 ± 0.10 mag and E(V-I) = 0.13 mag for the distance modulus and reddening of the LMC, respectively.