No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Abstract
We place direct upper limits on the amplitude of gravitational waves from 28 isolated radio pulsars by a coherent multidetector analysis of the data collected during the second science run of the LIGO interferometric detectors. These are the first direct upper limits for 26 of the 28 pulsars. We use coordinated radio observations for the first time to build radio-guided phase templates for the expected gravitational-wave signals. The unprecedented sensitivity of the detectors allows us to set strain upper limits as low as a few times 10(-24). These strain limits translate into limits on the equatorial ellipticities of the pulsars, which are smaller than 10(-5) for the four closest pulsars.
... The only unknowns in the signal model are therefore the gravitational wave amplitude at Earth, as given in Equation 1, and the orientation of the pulsar given by the inclination angle, ι, polarization angle, ψ, and relative phase at the epoch of the electromagnetic timing model, φ 0 . As in, e.g., [6,[9][10][11][12][13], following the method of [14], Bayesian inference can be used to produce a joint posterior probability density function on these four parameters, and the orientation parameters can be marginalized over to give a posterior on only h 0 . If the distance to a pulsar is known then this can be used to make inferences on, or set a limit on, the mass quadrupole moment, Q 22 , or alternatively, the pulsars fiducial ellipticity assuming a canonical moment of inertia of I zz = 10 38 kg m 2 [7]. ...
... In previous searches for known pulsars in gravitational wave data from the LIGO, Virgo and GEO600 detectors [6,[9][10][11][12][13] no signal has been seen, but upper limits, at a 95% credible level, were set on h 0 for all included pul-sars. In the latest results [13], using data from the first observing run (O1) of the advanced LIGO detectors [15], this produced limits on h 0 for 200 pulsars, which in turn gave limits on Q 22 and ε using the best-fit measured distances given in the ATNF Pulsar Catalogue [16]. ...
When looking for gravitational wave signals from known pulsars, targets have been treated using independent searches. Here we use a hierarchical Bayesian framework to combine observations from individual sources for two purposes: to produce a detection statistic for the whole ensemble of sources within a search, and, to estimate the hyperparameters of the underlying distribution of pulsar ellipticities. Both purposes require us to assume some functional form of the ellipticity distribution, and as a proof of principle we take two toy distributions. One is an exponential distribution,defined by its mean, and the other is a half-Gaussian distribution defined by its width. We show that by incorporating a common parameterized prior ellipticity distribution we can be more efficient at detecting gravitational waves from the whole ensemble of sources than trying to combine observations with a simpler non-hierarchical method. This may allow us to detect gravitational waves from the ensemble before there is confident detection of any single source. We also apply this method using data for 92 pulsars from LIGO's sixth science run. No evidence for a signal was seen, but 90\% upper limits of $3.9\ee{-8}$ and $4.7\ee{-8}$ were set on the mean of an assumed exponential ellipticity distribution and the width of an assumed half-Gaussian ellipticity distribution, respectively.
... These types of searches are referred to as targeted searches. The LIGO and Virgo Collaborations have already searched for this type of emission from known pulsars (both isolated and some in binaries) [11][12][13][14][15][16][17][18][19], for which accurate ephemerides were available. While for NSs observed as a central compact object of a supernova remnant or in a binary system, usually accurate ephemerides are not available. ...
Isolated spinning neutron stars, asymmetric with respect to their rotation axis, are expected to be sources of continuous gravitational waves. The most sensitive searches for these sources are based on accurate matched filtering techniques that assume the continuous wave to be phase locked with the pulsar beamed emission. While matched filtering maximizes the search sensitivity, a significant signal-to-noise ratio loss will happen in the case of a mismatch between the assumed and the true signal phase evolution. Narrow-band algorithms allow for a small mismatch in the frequency and spin-down values of the pulsar while coherently integrating the entire dataset. In this paper, we describe a narrow-band search using LIGO O2 data for the continuous wave emission of 33 pulsars. No evidence of a continuous wave signal is found, and upper limits on the gravitational wave amplitude over the analyzed frequency and spin-down ranges are computed for each of the targets. In this search, we surpass the spin-down limit, namely, the maximum rotational energy loss due to gravitational waves emission for some of the pulsars already present in the LIGO O1 narrow-band search, such as J1400−6325, J1813−1246, J1833−1034, J1952+3252, and for new targets such as J0940−5428 and J1747−2809. For J1400−6325, J1833−1034, and J1747−2809, this is the first time the spin-down limit is surpassed.
... b. S2-Known pulsars-BayesPE [78] A coherent targeted search for 28 known isolated radio pulsars was performed using the Bayesian parameterestimation pipline (BayesPE) on data from the second LIGO Science Run (S2), using 910 h of data from H1, 691 h from H2 and 342 h of L1 data from the S2 data set. ...
This paper presents an efficient numerical sensitivity-estimation method and implementation for continuous-gravitational-wave searches, extending and generalizing an earlier analytic approach by Wette [1]. This estimation framework applies to a broad class of F-statistic-based search methods, namely (i) semi-coherent StackSlide F-statistic (single-stage and hierarchical multistage), (ii) Hough number count on F-statistics, as well as (iii) Bayesian upper limits on F-statistic search results (coherent or semi-coherent). We test this estimate against results from Monte-Carlo simulations assuming Gaussian noise. We find the agreement to be within a few % at high detection (i.e., low false-alarm) thresholds, with increasing deviations at decreasing detection (i.e., higher false-alarm) thresholds, which can be understood in terms of the approximations used in the estimate. We also provide an extensive summary of sensitivity depths achieved in past continuous-gravitational-wave searches (derived from the published upper limits). For the F-statistic-based searches where our sensitivity estimate is applicable, we find an average relative deviation to the published upper limits of less than 10%, which in most cases includes systematic uncertainty about the noise-floor estimate used in the published upper limits.
... b. S2-Known pulsars-BayesPE [79] A coherent targeted search for 28 known isolated radio pulsars was performed using the Bayesian parameterestimation pipline (BayesPE) on data from the second LIGO Science Run (S2), using 910 h of data from H1, 691 h from H2 and 342 h of L1 data from the S2 data set. ...
This paper presents an efficient numerical sensitivity-estimation method and implementation for continuous-gravitational-wave searches, extending and generalizing an earlier analytic approach by Wette [1]. This estimation framework applies to a broad class of F-statistic-based search meth- ods, namely (i) semi-coherent StackSlide F-statistic (single-stage and hierarchical multi-stage), (ii) Hough number count on F-statistics, as well as (iii) Bayesian upper limits on (coherent or semi-coherent) F-statistic search results. We test this estimate against results from Monte-Carlo simulations assuming Gaussian noise. We find the agreement to be within a few % at high (i.e. low false-alarm) detection thresholds, with increasing deviations at decreasing (i.e. higher false- alarm) detection thresholds, which can be understood in terms of the approximations used in the estimate. We also provide an extensive summary of sensitivity depths achieved in past continuous- gravitational-wave searches (derived from the published upper limits). For the F-statistic-based searches where our sensitivity estimate is applicable, we find an average relative deviation to the published upper limits of less than 10%, which in most cases includes systematic uncertainty about the noise-floor estimate used in the published upper limits.
... Having multiple detectors located far apart is important for determining the sky location of the source (since the strain is three-dimensional). Although no detections have been made, LIGO has been able to place upper limits on the emission of GWs from ∼ 30 galactic pulsars(Abbott et al. 2005). It is anticipated that the planned upgrades of theLIGO detector to Advanced LIGO in 2014 could result in multiple and frequent direct detections. ...
Supermassive black holes permeate the observable Universe, residing in the nuclei of all or nearly all nearby massive galaxies and powering luminous quasars as far as ten billion light years away. These monstrous objects must grow through a combination of gas accretion and mergers of less massive black holes. The direct detection of the mergers by future gravitational-wave detectors will be a momentous scientific achievement, providing tests of general relativity and revealing the cosmic evolution of supermassive black holes. An additional --- and arguably equally rewarding --- challenge is the concomitant observation of merging supermassive black holes with both gravitational and electromagneticwaves. Such synergistic, "multi-messenger" studies can probe the expansion history of the Universe and shed light on the details of accretion astrophysics.
This thesis examines the mergers of supermassive black hole binaries and the observable signatures of these events. First, we consider the formation scenarios for the earliest supermassive black holes. This investigation is motivated by the Sloan Digital Sky Survey observation of a quasar that appears to be powered by a supermassive black hole with a mass of billions of solar masses, already in place one billion years after the Big Bang. Second, we develop semianalytic, time-dependent-models for the thermal emission from circumbinary gas disks around merging black holes. Our calculations corroborate the qualitative conclusion of a previous study that for black hole mergers detectable by a space-based gravitational-wave observatory, a gas disk near the merger remnant may exhibit a dramatic brightening of soft X-rays on timescales of several years. Our results suggest that this "afterglow" may become detectable more quickly after the merger than previously estimated. Third, we investigate whether these afterglow episodes could be observed serendipitously by forthcoming wide-field, high-cadence electromagnetic surveys. Fourth, we introduce a new subset of time-dependent solutions for the standard equation describing thin, viscous Keplerian disks. Finally, we apply these solutions to model the electromagnetic emission of accretion disks around supermassive black hole binaries that may be detectable with precision pulsar timing.
... Over the last decade several searches have looked for gravitational waves from a large selection of known pulsars using data from the LIGO, GEO 600 and Virgo gravitational wave detectors [1,2,3,4,5,6]. No evidence for signals has been observed, but these searches have produced upper limits on the gravitational wave amplitude for many pulsars by using Bayesian inference to calculate posterior probability distributions on the unknown signal parameters [7]. ...
We describe the consistency testing of a new code for gravitational wave
signal parameter estimation in known pulsar searches. The code uses an
implementation of nested sampling to explore the likelihood volume. Using fake
signals and simulated noise we compare this to a previous code that calculated
the signal parameter posterior distributions on both a grid and using a crude
Markov chain Monte Carlo (MCMC) method. We define a new parameterisation of two
orientation angles of neutron stars used in the signal model (the initial phase
and polarisation angle), which breaks a degeneracy between them and allows more
efficient exploration of those parameters. Finally, we briefly describe
potential areas for further study and the uses of this code in the future.
Now that detection of gravitational-wave signals from the coalescence of extra-galactic compact binary star mergers has become nearly routine, it is intriguing to consider other potential gravitational-wave signatures. Here we examine the prospects for discovery of continuous gravitational waves from fast-spinning neutron stars in our own galaxy and from more exotic sources. Potential continuous-wave sources are reviewed, search methodologies and results presented and prospects for imminent discovery discussed.
We present results of an all-sky search for continuous gravitational waves (CWs), which can be produced by fast spinning neutron stars with an asymmetry around their rotation axis, using data from the second observing run of the Advanced LIGO detectors. Three different semicoherent methods are used to search in a gravitational-wave frequency band from 20 to 1922 Hz and a first frequency derivative from −1×10−8 to 2×10−9 Hz/s. None of these searches has found clear evidence for a CW signal, so upper limits on the gravitational-wave strain amplitude are calculated, which for this broad range in parameter space are the most sensitive ever achieved.
Die Beobachtung der Sterne und Planeten hat eine viele tausend Jahre alte Tradition. Dies hat mehrere Gründe: Kaum jemand kann sich der Faszination entziehen, die der Anblick des Sternenhimmels auf den Beobachter ausübt. Die sich im Jahresrhythmus periodisch wiederholenden aber sonst scheinbar unveränderlichen Konstellationen der Sterne wecken im Menschen ein Gefühl der Ewigkeit, und es ist deshalb nicht verwunderlich, dass der Himmel mit dem Sitz der Götter identifiziert wurde, die von dort oben das Geschick der Menschen lenken. Deshalb war eine der Aufgaben der Astronomie bis zu Keplers Zeiten die Erstellung von Horoskopen (nach denen sich die Staatsmänner auch richteten). Auch heute noch gibt es viele Leute, die an den Einfluss der Sterne auf ihr Schicksal glauben, wozu allerdings die Astronomen nicht mehr gehören.
Ein weiterer, mehr praktischer Grund für das Interesse an der Astronomie war ihre Bedeutung für die Navigation auf See, für die Zeitrechnung und die Vorhersage periodischer, jahreszeitlich bedingter für die Menschen wichtiger Naturereignisse, wie z. B. die Nilflut oder die Monsunregen in Asien oder von besonderen Ereignissen am Himmel, wie Sonnen- und Mondfinsternisse.
We present a review of modern optical techniques being used and developed for
the field of gravitational wave detection. We describe the current
state-of-the-art of gravitational waves detector technologies with regard to
optical layouts, suspensions and test masses. We discuss the dominant sources
and noise in each of these subsystems and the developments that will help
mitigate them for future generations of detectors. We very briefly summarise
some of the novel astrophysics that will be possible with these upgraded
detectors.
adenocarcinoma of the lower rectum is technically challenging due to the conflict between wide excision to achieve oncological clearance and sphincter conservation to maintain anal function. A national low rectal cancer development programme (LOREC) was developed under the auspices of the Association of Coloproctology of Great Britain and Ireland and the English National Cancer Action Team to improve the outcome of low rectal cancer in England.
a low rectal cancer development programme was initiated focusing on pre-operative imaging, selective neoadjuvant therapy, optimal surgical treatment and detailed pathological assessment of the excised specimen. Its key elements were one day MDT workshops, cadaveric surgical training, surgical mentoring, pathological audit and radiological workshops.
overall 147(89.6%) of 164 MDTs from 151 NHS Trusts (some with two MDTs) in England participated in 15 workshops in Basingstoke or Leeds. In addition 112 surgeons attended a one day cadaveric training programme in Bristol, Newcastle or Nottingham with the main focus on extra-levator APE (ELAPE), and pelvic reconstruction, with input from anatomists, colorectal and plastic surgeons.
optimal staging, selective preoperative chemoradiotherapy and precise surgery were considered crucial to improve the outcome for patients with low rectal cancer. This article is protected by copyright. All rights reserved.
Significant progress has been made in recent years on the development of
gravitational wave detectors. Sources such as coalescing compact binary
systems, neutron stars in low-mass X-ray binaries, stellar collapses and
pulsars are all possible candidates for detection. The most promising design of
gravitational wave detector uses test masses a long distance apart and freely
suspended as pendulums on Earth or in drag-free craft in space. The main theme
of this review is a discussion of the mechanical and optical principles used in
the various long baseline systems in operation around the world - LIGO (USA),
Virgo (Italy/France), TAMA300 and LCGT (Japan), and GEO600 (Germany/U.K.) - and
in LISA, a proposed space-borne interferometer. A review of recent science runs
from the current generation of ground-based detectors will be discussed, in
addition to highlighting the astrophysical results gained thus far. Looking to
the future, the major upgrades to LIGO (Advanced LIGO), Virgo (Advanced Virgo),
LCGT and GEO600 (GEO-HF) will be completed over the coming years, which will
create a network of detectors with significantly improved sensitivity required
to detect gravitational waves. Beyond this, the concept and design of possible
future "third generation" gravitational wave detectors, such as the Einstein
Telescope (ET), will be discussed.
Membrane fusion plays a central role in many cell processes from vesicular transport to nuclear envelope reconstitution at mitosis but the mechanisms that underlie fusion of natural membranes are not well understood. Studies with synthetic membranes and theoretical considerations indicate that accumulation of lipids characterised by negative curvature such as diacylglycerol (DAG) facilitate fusion. However, the specific role of lipids in membrane fusion of natural membranes is not well established. Nuclear envelope (NE) assembly was used as a model for membrane fusion. A natural membrane population highly enriched in the enzyme and substrate needed to produce DAG has been isolated and is required for fusions leading to nuclear envelope formation, although it contributes only a small amount of the membrane eventually incorporated into the NE. It was postulated to initiate and regulate membrane fusion. Here we use a multidisciplinary approach including subcellular membrane purification, fluorescence spectroscopy and Förster resonance energy transfer (FRET)/two-photon fluorescence lifetime imaging microscopy (FLIM) to demonstrate that initiation of vesicle fusion arises from two unique sites where these vesicles bind to chromatin. Fusion is subsequently propagated to the endoplasmic reticulum-derived membranes that make up the bulk of the NE to ultimately enclose the chromatin. We show how initiation of multiple vesicle fusions can be controlled by localised production of DAG and propagated bidirectionally. Phospholipase C (PLCgamma), GTP hydrolysis and (phosphatidylinsositol-(4,5)-bisphosphate (PtdIns(4,5)P(2)) are required for the latter process. We discuss the general implications of membrane fusion regulation and spatial control utilising such a mechanism.
Gravitational wave detectors are already operating at interesting sensitivity
levels, and they have an upgrade path that should result in secure detections
by 2014. We review the physics of gravitational waves, how they interact with
detectors (bars and interferometers), and how these detectors operate. We study
the most likely sources of gravitational waves and review the data analysis
methods that are used to extract their signals from detector noise. Then we
consider the consequences of gravitational wave detections and observations for
physics, astrophysics, and cosmology.
Wavefront distortion due to absorption in the substrates and coatings of mirrors in advanced gravitational wave interferometers has the potential to compromise the operation and sensitivity of these interferometers [Opt. Lett.29, 2635-2637 (2004)]. We report the first direct spatially-resolved measurement, to our knowledge, of such wavefront distortion in a high optical power cavity. The measurement was made using an ultrahigh sensitivity Hartmann wavefront sensor on a dedicated test facility. The sensitivity of the sensor was lambda/730, where lambda=800 nm.
I make the first estimates of maximum elastic quadrupole deformations sustainable by alternatives to conventional neutron stars. Solid strange quark stars might sustain maximum ellipticities (dimensionless quadrupoles) up to a few times rather than a few times for conventional neutron stars, and hybrid quark-baryon or meson-condensate stars might sustain up to . Most of the difference is due to the shear modulus, which can be up to rather than in the inner crust of a conventional neutron star. Maximum solid strange star ellipticities are comparable to upper limits obtained for several known pulsars in a recent gravitational-wave search by LIGO. Maximum ellipticities of the more robust hybrid model will be detectable by LIGO at initial design sensitivity. A large shear modulus also strengthens the case for starquakes as an explanation for frequent pulsar glitches.
In an experiment to simulate the conditions in high optical power advanced gravitational wave detectors, we show for the first time that the time evolution of strong thermal lenses follows the predicted infinite sum of exponentials (approximated by a double exponential), and that such lenses can be compensated using an intracavity compensation plate heated on its cylindrical surface. We show that high finesse approximately 1400 can be achieved in cavities with internal compensation plates, and that mode matching can be maintained. The experiment achieves a wave front distortion similar to that expected for the input test mass substrate in the Advanced Laser Interferometer Gravitational Wave Observatory, and shows that thermal compensation schemes are viable. It is also shown that the measurements allow a direct measurement of substrate optical absorption in the test mass and the compensation plate.
The present quantitative model for Galactic free electron distribution abandons the assumption of axisymmetry and explicitly incorporates spiral arms; their shapes and locations are derived from existing radio and optical observations of H II regions. The Gum Nebula's dispersion-measure contributions are also explicitly modeled. Adjustable quantities are calibrated by reference to three different types of data. The new model is estimated to furnish distance estimates to known pulsars that are accurate to about 25 percent.
- M Pitkin
- G Woan
M. Pitkin and G. Woan, Classical and Quantum Gravity
21 S843 (2004).
- P Jaranowski
- A Królak
- B Schutz
P. Jaranowski, A. Królak and B. Schutz, Phys. Rev. D
58 063001 (1998).
- T Suzuki
T. Suzuki, in First Edoardo Amaldi Conference on
Gravitational Wave Experiments, edited by E. Coccia,
G. Pizzella and F. Ronga (World Scientific, Singapore,
1995), p. 115.
Mitselmakher, 34 R. Mittleman, 13 O. Miyakawa, 12 S. Miyoki, 12, w S. Mohanty, 29 G
- P Mitrofanov
P. Mitrofanov, 20 G. Mitselmakher, 34 R. Mittleman, 13 O. Miyakawa, 12 S. Miyoki, 12, w S. Mohanty, 29 G. Moreno, 14
K. Mossavi, 2 G. Mueller, 34 S. Mukherjee, 29 P. Murray, 35 J. Myers, 14 S. Nagano, 2 T. Nash, 12 R. Nayak, 11
Bullington, 26 A. Bunkowski, 2, 31 A. Buonanno, 6, g R. Burgess, 13 D
- A Brown
A. Brown, 39 A. Bullington, 26 A. Bunkowski, 2, 31 A. Buonanno, 6, g R. Burgess, 13 D. Busby, 12 W. E. Butler, 38
R. L. Byer, 26 L. Cadonati, 13 G. Cagnoli, 35 J. B. Camp, 21 C. A. Cantley, 35 L. Cardenas, 12 K. Carter, 15
29 D. I. Jones, 28 L. Jones, 12 D
- W W Ito
- W R Johnson
- Johnston
Ito, 37 Y. Itoh, 1 A. Ivanov, 12 O. Jennrich, 35, q B. Johnson, 14 W. W. Johnson, 16 W. R. Johnston, 29 D. I. Jones, 28
L. Jones, 12 D. Jungwirth, 12, r V. Kalogera, 23 E. Katsavounidis, 13 K. Kawabe, 14 S. Kawamura, 22 W. Kells, 12
J. Kern, 15, s A. Khan, 15 S. Killbourn, 35 C. J. Killow, 35 C. Kim, 23 C. King, 12 P. King, 12 S. Klimenko, 34
14 B. Bochner, 13, f L. Bogue, 12 R
- B Bland
B. Bland, 14 B. Bochner, 13, f L. Bogue, 12 R. Bork, 12 S. Bose, 40 P. R. Brady, 39 V. B. Braginsky, 20 J. E. Brau, 37
Araya, 12 H. Armandula, 12 M. Ashley, 28 F. Asiri, 12, a P
- G Anderson
G. Anderson, 29 M. Araya, 12 H. Armandula, 12 M. Ashley, 28 F. Asiri, 12, a P. Aufmuth, 31 C. Aulbert, 1
Frey, 37 P. Fritschel, 13 V
- Y Franzen
Y. Franzen, 34 A. Freise, 2, l R. Frey, 37 P. Fritschel, 13 V. V. Frolov, 15 M. Fyffe, 15 K. S. Ganezer, 5 J. Garofoli, 14
J. A. Giaime, 16 A. Gillespie, 12, m K. Goda, 13 G. González, 16 S. Goßler, 31 P. Grandclément, 23, n A. Grant, 35
C. Gray, 14 A. M. Gretarsson, 15 D. Grimmett, 12 H. Grote, 2 S. Grunewald, 1 M. Guenther, 14 E. Gustafson, 26, o
R. Gustafson, 36 W. O. Hamilton, 16 M. Hammond, 15 J. Hanson, 15 C. Hardham, 26 J. Harms, 19 G. Harry, 13