[gr-qc/0503121] LISA source confusion: identification and characterization of signals

Authors: Richard Umstaetter, Nelson Christensen, Martin Hendry, Renate Meyer, Vimal Simha, John Veitch, Sarah Vigeland, Graham Woan

Date: Wed, 30 Mar 2005

Abstract: The Laser Interferometer Space Antenna (LISA) is expected to detect gravitational radiation from a large number of compact binary systems. We present a method by which these signals can be identified and have their parameters estimated. Our approach uses Bayesian inference, specifically the application of a Markov chain Monte Carlo method. The simulation study that we present here considers a large number of sinusoidal signals in noise, and our method estimates the number of periodic signals present in the data, the parameters for these signals and the noise level. The method is significantly better than classical spectral techniques at performing these tasks and does not use stopping criteria for estimating the number of signals present.

abs pdf

Mar 31, 2005

0503121 (/preprints/gr-qc)
2005-03-31, 09:12 [edit]


[gr-qc/0503119] Merger of binary neutron stars with realistic equations of state in full general relativity

Authors: Masaru Shibata, Keisuke Taniguchi, Koji Uryu

Date: Wed, 30 Mar 2005

Abstract: We present numerical results of three-dimensional simulations for the merger of binary neutron stars (BNSs) in full general relativity. Hybrid equations of state (EOSs) are adopted to mimic realistic nuclear EOSs. In this approach, we divide the EOSs into two parts, i.e., the thermal part and the cold part. For the cold part, we assign a fitting formula for realistic EOSs of cold nuclear matter slightly modifying the formula developed by Haensel and Potekhin. We adopt the SLy and FPS EOSs for which the maximum allowed ADM mass of cold and spherical neutron stars (NSs) is ~ 2.04Mo and 1.80Mo, respectively. Simulations are performed for BNSs of the total ADM mass in the range between 2.4Mo and 2.8Mo with the rest-mass ratio Q_M to be in the range 0.9 < Q_M < 1. It is found that if the total ADM mass of the system is larger than a threshold M_{thr}, a black hole (BH) is promptly formed in the merger irrespective of the mass ratios. In the other case, the outcome is a hypermassive NS of a large ellipticity, which results from the large adiabatic index of the realistic EOSs adopted. The value of M_{thr} depends on the EOS: ~ 2.7Mo and ~ 2.5Mo for the SLy and FPS EOSs, respectively. Gravitational waves are computed in terms of a gauge-invariant wave extraction technique. In the formation of the hypermassive NS, quasiperiodic gravitational waves of a large amplitude and of frequency between 3 and 4 kHz are emitted. The estimated emission time scale is < 100 ms, after which the hypermassive NS collapses to a BH. Because of the long emission time, the effective amplitude may be large enough to be detected by advanced laser interferometric gravitational wave detectors if the distance to the source is smaller than ~ 100 Mpc.

abs pdf

Mar 31, 2005

0503119 (/preprints/gr-qc)
2005-03-31, 09:11 [edit]


[gr-qc/0501041] The basics of gravitational wave theory

Authors: Eanna E. Flanagan, Scott A. Hughes

Date: Wed, 12 Jan 2005

Abstract: Einstein's special theory of relativity revolutionized physics by teaching us that space and time are not separate entities, but join as ‘spacetime’. His general theory of relativity further taught us that spacetime is not just a stage on which dynamics takes place, but is a participant: The field equation of general relativity connects matter dynamics to the curvature of spacetime. Curvature is responsible for gravity, carrying us beyond the Newtonian conception of gravity that had been in place for the previous two and a half centuries. Much research in gravitation since then has explored and clarified the consequences of this revolution; the notion of dynamical spacetime is now firmly established in the toolkit of modern physics. Indeed, this notion is so well established that we may now contemplate using spacetime as a tool for other science. One aspect of dynamical spacetime -- its radiative character, ‘gravitational radiation’ -- will inaugurate entirely new techniques for observing violent astrophysical processes. Over the next one hundred years, much of this subject's excitement will come from learning how to exploit spacetime as a tool for astronomy. This article is intended as a tutorial in the basics of gravitational radiation physics.

abs pdf

Mar 22, 2005

0501041 (/preprints/gr-qc)
2005-03-22, 18:28 [edit]


[gr-qc/0503086] Matters of Gravity, the newsletter of the Topical Group on Gravitation of the Americal Physical Society

Authors: Jorge Pullin

Date: Sun, 20 Mar 2005

Abstract: GGR News:
Message from the Chair, by Jim Isenberg
Einstein@Home, by Bernard Schutz
We hear that…, by Jorge Pullin
100 Years ago, by Jorge Pullin
Research Briefs:
What's new in LIGO, by David Shoemaker
Frame-dragging in the news in 2004, by Cliff Will
Cosmic (super)strings and LIGO, by Xavier Siemens
Conference reports:
The first gulf coast gravity conference, by Richard Price
Imagining the future, by Shane Larson
VI Mexican School, by Alejandro Corichi

abs pdf

Mar 22, 2005

0503086 (/preprints/gr-qc)
2005-03-22, 08:46 [edit]


[astro-ph/0503386] Testing GR with the Double Pulsar: Recent Results

Authors: M. Kramer, D. R. Lorimer, A. G. Lyne, M. McLaughlin, M.Burgay, N. D'Amico, A. Possenti, F. Camilo, P. C. C. Freire, B. C. Joshi, R. N. Manchester, J. Reynolds, J. Sarkissian, I. H. Stairs, R. D. Ferdman

Date: Thu, 17 Mar 2005

Abstract: This first ever double pulsar system consists of two pulsars orbiting the common center of mass in a slightly eccentric orbit of only 2.4-hr duration. The pair of pulsars with pulse periods of 22 ms and 2.8 sec, respectively, confirms the long-proposed recycling theory for millisecond pulsars and provides an exciting opportunity to study the works of pulsar magnetospheres by a very fortunate geometrical alignment of the orbit relative to our line-of-sight. In particular, this binary system represents a truly unique laboratory for relativistic gravitational physics. This contribution serves as an update on the currently obtained results and their consequences for the test of general relativity in the strong-field regime. A complete and more up-to-date report of the timing results will be presented elsewhere shortly.

abs pdf

Mar 21, 2005

0503386 (/preprints/astro-ph)
2005-03-21, 12:00 [edit]


[gr-qc/0503069] General covariance and the objectivity of space-time point-events

Authors: L. Lusanna, M. Pauri

Date: Wed, 16 Mar 2005

Abstract: "The last remnant of physical objectivity of space-time" is disclosed, beyond the Leibniz equivalence, in the case of a continuous family of spatially non-compact models of general relativity. The physical individuation of point-events is furnished by the intrinsic degrees of freedom of the gravitational field, (viz, the Dirac observables) that represent - as it were - the ontic part of the metric field. The physical role of the epistemic part (viz. the gauge variables) is likewise clarified. At the end, a peculiar four-dimensional holistic and structuralist view of space-time emerges which includes elements common to the tradition of both substantivalism and relationism. The observables of our models undergo real temporal change and thereby provide a counter-example to the thesis of the frozen-time picture of evolution. Invited Contribution to the ESF 2004 Oxford Conference on Space-Time.

abs pdf

Mar 21, 2005

0503069 (/preprints/gr-qc)
2005-03-21, 11:58 [edit]


[gr-qc/0503066] A Michelson Interferometer in the Field of a Plane Gravitational Wave

Authors: Nikodem J. Poplawski

Date: Wed, 16 Mar 2005

Abstract: In this paper we treat the problem of a Michelson interferometer in the field of a weak, monochromatic, plane gravitational wave in the framework of the general theory of relativity. The arms of the interferometer are regarded as world lines, whose motion is determined by the equations of geodesics in the Hamilton-Jacobi formalism. We find that interference appears in the second approximation. Moreover, the measurement of the light beam delay between both arms can be used for determining the wavelength of such a wave.

abs pdf

Mar 21, 2005

0503066 (/preprints/gr-qc)
2005-03-21, 11:56 [edit]


[astro-ph/0503287] Gravitational Radiation from an Accreting Millisecond Pulsar with a Magnetically Confined Mountain

Authors: A. Melatos, D. J. B. Payne

Date: Mon, 14 Mar 2005

Abstract: The amplitude of the gravitational radiation from an accreting neutron star undergoing polar magnetic burial is calculated. During accretion, the magnetic field of a neutron star is compressed into a narrow belt at the magnetic equator by material spreading equatorward from the polar cap. In turn, the compressed field confines the accreted material in a polar mountain which is misaligned with the rotation axis in general, producing gravitational waves. The equilibrium hydromagnetic structure of the polar mountain, and its associated mass quadrupole moment, are computed as functions of the accreted mass, M_a, by solving a Grad-Shafranov boundary value problem. The orientation- and polarization-averaged gravitational wave strain, h_c ~ 6e-24 for a 0.6 kHz source at 1 kpc with M_a > 10ˆ-5 M_Sun, exceeds previous estimates that failed to treat equatorward spreading and flux freezing self-consistently. It is concluded that an accreting millisecond pulsar emits a persistent, sinusoidal gravitational wave signal at levels detectable, in principle, by long baseline interferometers after phase-coherent integration, provided that the polar mountain is hydromagnetically stable. Magnetic burial also reduces the magnetic dipole moment, mu, monotonically, implying a novel, observationally testable scaling h_c(mu). The implications for the rotational evolution of (accreting) X-ray and (isolated) radio millisecond pulsars are explored.

abs pdf

Mar 19, 2005

0503287 (/preprints/astro-ph)
2005-03-19, 14:24 [edit]


[astro-ph/0410343] The Afterglow of Massive Black Hole Coalescence

Authors: Milos Milosavljevic, E. S. Phinney (Caltech)

Date: Mon, 14 Mar 2005

Abstract: The final merger of a pair of massive black holes in a galactic nucleus is compelled by gravitational radiation. Gravitational waves from the mergers of black holes of masses (10ˆ5-10ˆ7)(1+z)ˆ{-1} Msun at redshifts of 1-20 will be readily detectable by the Laser Interferometer Space Antenna (LISA), but an electromagnetic afterglow would be helpful in pinpointing the source and its redshift. Long before the merger, the binary "hollows out" any surrounding gas and shrinks slowly compared to the viscous timescale of a circumbinary disk. The inner gas disk is truncated at the radius where gravitational torque from the binary balances the viscous torque, and accretion onto the black holes is diminished. Initially, the inner truncation radius is able to follow the shrinking binary inward. But eventually the gravitational radiation timescale becomes shorter than the viscous timescale in the disk, leading to a merged black hole surrounded by a hollow disk of gas. We show that the subsequent viscous evolution of the hollow, radiation-pressure dominated disk will create a ~10ˆ{43.5}(M/10ˆ6Msun) ergs sˆ{-1} X-ray source on a timescale \~7(1+z)(M/10ˆ6Msun)ˆ{1.32} yr. This justifies follow-up monitoring of gravitational wave events with next-generation X-ray observatories. Analysis of the detailed light curve of these afterglows will yield new insights into the subtle physics of accretion onto massive black holes.

abs pdf

Mar 19, 2005

0410343 (/preprints/astro-ph)
2005-03-19, 14:23 [edit]


[gr-qc/0503021] A Route to Understanding of the Pioneer Anomaly

Authors: Slava G. Turyshev, Michael Martin Nieto, John D. Anderson

Date: Fri, 4 Mar 2005

Abstract: The Pioneer 10 and 11 spacecraft yielded the most precise navigation in deep space to date. However, while at heliocentric distance of $\sim$ 20--70 AU, the accuracies of their orbit reconstructions were limited by a small, anomalous, Doppler frequency drift. This drift can be interpreted as a sunward constant acceleration of $a_P = (8.74 \pm 1.33)\times 10ˆ{-8}$ cm/s$ˆ2$ which is now commonly known as the Pioneer anomaly. Here we discuss the Pioneer anomaly and present the next steps towards understanding of its origin. They are: 1) Analysis of the entire set of existing Pioneer 10 and 11 data, obtained from launch to the last telemetry received from Pioneer 10, on 27 April 2002, when it was at a heliocentric distance of 80 AU. This data could yield critical new information about the anomaly. If the anomaly is confirmed, 2) Development of an instrumental package to be operated on a deep space mission to provide an independent confirmation on the anomaly. If further confirmed, 3) Development of a deep-space experiment to explore the Pioneer anomaly in a dedicated mission with an accuracy for acceleration resolution at the level of $10ˆ{-10}$ cm/s$ˆ2$ in the extremely low frequency range. In Appendices we give a summary of the Pioneer anomaly's characteristics, outline in more detail the steps needed to perform an analysis of the entire Pioneer data set, and also discuss the possibility of extracting some useful information from the Cassini mission cruise data.

abs pdf

Mar 07, 2005

0503021 (/preprints/gr-qc)
2005-03-07, 21:22 [edit]


[gr-qc/0503016] Gravitational-Wave Emission from Rotating Gravitational Collapse in three Dimensions

Authors: L. Baiotti, I. Hawke, L. Rezzolla, E. Schnetter

Date: Fri, 4 Mar 2005

Abstract: We present the first calculation of gravitational wave emission produced in the gravitational collapse of uniformly rotating neutron stars to black holes in fully three-dimensional simulations. The initial stellar models are relativistic polytropes which are dynamically unstable and with angular velocities ranging from slow rotation to the mass-shedding limit. An essential aspect of these simulations is the use of progressive mesh-refinement techniques which allow to move the outer boundaries of the computational domain to regions where gravitational radiation attains its asymptotic form. The waveforms have been extracted using a gauge-invariant approach in which the numerical spacetime is matched with the non-spherical perturbations of a Schwarzschild spacetime. Overall, the results indicate that the waveforms have features related to the properties of the initial stellar models (in terms of their w-mode oscillations) and of the newly produced rotating black holes (in terms of their quasi-normal modes). While our waveforms are in good qualitative agreement with those computed by Stark and Piran in two-dimensional simulations, our amplitudes are about one order of magnitude smaller and this difference is mostly likely due to our less severe pressure reduction. For a neutron star rotating uniformly near mass-shedding and collapsing at 10 kpc, the signal-to-noise ratio computed uniquely from the burst is S/N ~ 0.25, but this grows to be S/N <~ 4 in the case of LIGO II.

abs pdf

Mar 07, 2005

0503016 (/preprints/gr-qc)
2005-03-07, 10:55 [edit]


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