[1102.4830] Magnetar Asteroseismology with Long-Term Gravitational Waves

Authors: Kazumi Kashiyama, Kunihito Ioka

Date: 23 Feb 2011

Abstract: Magnetic flares and induced oscillations of magnetars (super-magnetized neutron stars) are promising sources of gravitational waves (GWs). We suggest that the GW emission, if any, would last longer than the observed X-ray quasi-periodic oscillations (X-QPOs), calling for the longer-term GW analyses from a day to months than the current searches. Like the pulsar timing, the oscillation frequency would also evolve with time because of the decay or reconfiguration of magnetic field, which is crucial for the GW detection. With the observed GW frequency and its time-derivatives, we can probe the interior magnetic field strength and its evolution to open a new GW asteroseismology with the next generation interferometers like advanced LIGO, advanced VIRGO, LCGT and ET.

abs pdf

Feb 28, 2011

1102.4830 (/preprints)
2011-02-28, 23:28 [edit]


[1102.4855] Fast coalescence of massive black hole binaries from mergers of galactic nuclei: implications for low-frequency gravitational-wave astrophysics

Authors: Miguel Preto, Ingo Berentzen, Peter Berczik, Rainer Spurzem

Date: 23 Feb 2011

Abstract: We investigate a purely stellar dynamical solution to the Final Parsec Problem. Galactic nuclei resulting from major mergers are not spherical, but show some degree of triaxiality. With $N$-body simulations, we show that massive black hole binaries (MBHB) hosted by them will continuously interact with stars on centrophilic orbits and will thus inspiral — in much less than a Hubble time — down to separations at which gravitational wave (GW) emission is strong enough to drive them to coalescence. Such coalescences will be important sources of GWs for future space-borne detectors such as the {\it Laser Interferometer Space Antenna} (LISA). Based on our results, we expect that LISA will see between $\sim 10$ to $\sim {\rm few} \times 10ˆ2$ such events every year, depending on the particular MBH seed model as obtained in recent studies of merger trees of galaxy and MBH co-evolution. Orbital eccentricities in the LISA band will be clearly distinguishable from zero with $e \gtrsim 0.001-0.01$.

abs pdf

Feb 28, 2011

1102.4855 (/preprints)
2011-02-28, 23:28 [edit]


[1102.4965] Numerical simulation of time delay interferometry for LISA with one arm dysfunctional

Authors: S. V. Dhurandhar, W.-T. Ni, G. Wang

Date: 24 Feb 2011

Abstract: In order to attain the requisite sensitivity for LISA, laser frequency noise must be suppressed below the secondary noises such as the optical path noise, acceleration noise etc. In a previous paper (Dhurandhar et al., Class. Quantum Grav., 27, 135013, 2010), we have found a large family of second generation analytic solutions of time delay interferometry with one arm dysfunctional and also estimated the laser noise due to residual time-delay semi-analytically from orbit perturbations due to Earth. Since other planets and solar-system bodies also perturb the orbits of LISA spacecraft and affect the time delay interferometry (TDI), we simulate the time delay numerically in this paper for all solutions with n \leq 3. To conform to the actual LISA planning, we have worked out a set of 3-year optimized mission orbits of LISA spacecraft starting at June 21, 2021 using CGC2.7 ephemeris framework. We then use this numerical solution to calculate the residual optical path differences in the second generation solutions of our previous paper, and compare with the semi-analytic error estimate. The accuracy of this calculation is better than 1 cm (or 30 ps). The maximum path length difference, for all configuration calculated, is below 1 m (3 ns). This is well below the limit under which the laser frequency noise is required to be suppressed.

abs pdf

Feb 28, 2011

1102.4965 (/preprints)
2011-02-28, 23:28 [edit]


[1102.5646] Evidence for gravitational quadrupole moment variations in the companion of PSR J2051-0827

Authors: K. Lazaridis, J.P.W. Verbiest, T.M. Tauris, B.W. Stappers, M. Kramer, N. Wex, A. Jessner, I. Cognard, G. Desvignes, G.H. Janssen, M.B. Purver, G. Theureau, C.G. Bassa, R. Smits

Date: 28 Feb 2011

Abstract: We have conducted radio timing observations of the eclipsing millisecond binary pulsar J2051-0827 with the European Pulsar Timing Array network of telescopes and the Parkes radio telescope, spanning over 13 years. The increased data span allows significant measurements of the orbital eccentricity, e = (6.2 {\pm} 1.3) {\times} 10ˆ{-5} and composite proper motion, {\mu}_t = 7.3 {\pm} 0.4 mas/yr. Our timing observations have revealed secular variations of the projected semi-major axis of the pulsar orbit which are much more extreme than those previously published; and of the orbital period of the system. Investigation of the physical mechanisms producing such variations confirm that the variations of the semi-major axis are most probably caused by classical spin-orbit coupling in the binary system, while the variations in orbital period are most likely caused by tidal dissipation leading to changes in the gravitational quadrupole moment of the companion.

abs pdf

Feb 28, 2011

1102.5646 (/preprints)
2011-02-28, 23:27 [edit]


[1102.5470] Observability of pulsar beam bending by the Sgr~A* black hole

Authors: Kevin Stovall, Teviet Creighton, Richard H. Price, Fredrick A. Jenet

Date: 27 Feb 2011

Abstract: According to some models, there may be a significant population of radio pulsars in the Galactic center. In principle, a beam from one of these pulsars could pass close to the supermassive black hole (SMBH) at the center, be deflected, and be detected by Earth telescopes. Such a configuration would be an unprecedented probe of the properties of spacetime in the moderate- to strong-field regime of the SMBH. We present here background on the problem, and approximations for the probability of detection of such beams. We conclude that detection is marginally probable with current telescopes, but that telescopes that will be operating in the near future, with an appropriate multiyear observational program, will have a good chance of detecting a beam deflected by the SMBH.

abs pdf

Feb 28, 2011

1102.5470 (/preprints)
2011-02-28, 23:27 [edit]


[1102.5340] Arecibo PALFA Survey and Einstein@Home: Binary Pulsar Discovery by Volunteer Computing

Authors: B. Knispel, P. Lazarus, B. Allen, D. Anderson, C. Aulbert, N. D. R. Bhat, O. Bock, S. Bogdanov, A. Brazier, F. Camilo, S. Chatterjee, J. M. Cordes, F. Crawford, J. S. Deneva, G. Desvignes, H. Fehrmann, P. C. C. Freire, D. Hammer, J. W. T. Hessels, F. A. Jenet, V. M. Kaspi, M. Kramer, J. van Leeuwen, D. R. Lorimer, A. G. Lyne, B. Machenschalk, M. A. McLaughlin, C. Messenger, D. J. Nice, M. A. Papa, H. J. Pletsch, R. Prix, S. M. Ransom, X. Siemens, I. H. Stairs, B. W. Stappers, K. Stovall, A. Venkataraman

Date: 25 Feb 2011

Abstract: We report the discovery of the 20.7-ms binary pulsar J1952+2630, made using the distributed computing project Einstein@Home in Pulsar ALFA survey observations with the Arecibo telescope. Follow-up observations with the Arecibo telescope confirm the binary nature of the system. We obtain a circular orbital solution with an orbital period of 9.4 hr, a projected orbital radius of 2.8 lt-s, and a mass function of f = 0.15 solar masses by analysis of spin period measurements. No evidence of orbital eccentricity is apparent; we set a 2-sigma upper limit e < 1.7e-3. The orbital parameters suggest a massive white dwarf companion with a minimum mass of 0.95 solar masses, assuming a pulsar mass of 1.4 solar masses. Most likely, this pulsar belongs to the rare class of intermediate mass binary pulsars. Future timing observations will aim to determine the parameters of this system further, measure relativistic effects, and elucidate the nature of the companion star.

abs pdf

Feb 28, 2011

1102.5340 (/preprints)
2011-02-28, 23:27 [edit]


[1102.5192] On the unreasonable effectiveness of the post-Newtonian approximation in gravitational physics

Authors: Clifford M. Will

Date: 25 Feb 2011

Abstract: The post-Newtonian approximation is a method for solving Einstein's field equations for physical systems in which motions are slow compared to the speed of light and where gravitational fields are weak. Yet it has proven to be remarkably effective in describing certain strong-field, fast-motion systems, including binary pulsars containing dense neutron stars and binary black hole systems inspiraling toward a final merger. The reasons for this effectiveness are largely unknown. When carried to high orders in the post-Newtonian sequence, predictions for the gravitational-wave signal from inspiraling compact binaries will play a key role in gravitational-wave detection by laser-interferometric observatories.

abs pdf

Feb 28, 2011

1102.5192 (/preprints)
2011-02-28, 23:12 [edit]


[1102.5332] Binary Inspirals in Nordstr\"om's Second Theory

Authors: Travis Garrett

Date: 25 Feb 2011

Abstract: We investigate Nordstr\"om's second theory of gravitation, with a focus on utilizing it as a testbed for developing techniques in numerical relativity. Numerical simulations of inspiraling compact star binaries are performed for this theory, and compared to the predictions of semi-analytic calculations (which are similar to Peters and Mathews' results for GR). The simulations are based on a co-rotating spherical coordinate system, where both finite difference and pseudo-spectral methods are used. We also adopt the "Hydro without Hydro" approximation, and the Weak Radiation Reaction approximation when the orbital motion is quasi-circular. We evolve a binary with quasi-circular initial data for hundreds of orbits and find that the resulting inspiral closely matches the ¼ power law profile given by the semi-analytical calculations. We additionally find that an eccentric binary circularizes and precesses at the expected rates. The methods investigated thus provide a promising line of attack for the numerical modeling of long binary inspirals in general relativity.

abs pdf

Feb 28, 2011

1102.5332 (/preprints)
2011-02-28, 23:12 [edit]


[1102.5094] Reassessing The Fundamentals: New Constraints on the Evolution, Ages and Masses of Neutron Stars

Authors: Bulent Kiziltan

Date: 24 Feb 2011

Abstract: The ages and masses of neutron stars (NSs) are two fundamental threads that make pulsars accessible to other sub-disciplines of astronomy and physics. A realistic and accurate determination of these two derived parameters play an important role in understanding of advanced stages of stellar evolution and the physics that govern relevant processes. Here I summarize new constraints on the ages and masses of NSs with an evolutionary perspective. I show that the observed P-Pdot demographics is more diverse than what is theoretically predicted for the standard evolutionary channel. In particular, standard recycling followed by dipole spin-down fails to reproduce the population of millisecond pulsars with higher magnetic fields (B > 4 x 10ˆ{8} G) at rates deduced from observations. A proper inclusion of constraints arising from binary evolution and mass accretion offers a more realistic insight into the age distribution. By analytically implementing these constraints, I propose a "modified" spin-down age for millisecond pulsars that gives estimates closer to the true age. Finally, I independently analyze the peak, skewness and cutoff values of the underlying mass distribution from a comprehensive list of radio pulsars for which secure mass measurements are available. The inferred mass distribution shows clear peaks at 1.35 Msun and 1.50 Msun for NSs in double neutron star (DNS) and neutron star-white dwarf (NS-WD) systems respectively. I find a mass cutoff at 2 Msun for NSs with WD companions, which establishes a firm lower bound for the maximum mass of NSs.

abs pdf

Feb 28, 2011

1102.5094 (/preprints)
2011-02-28, 23:11 [edit]


[1102.4654] Designing a cross-correlation search for continuous-wave gravitational radiation from a neutron star in the supernova remnant SNR 1987A

Authors: Christine Chung, Andrew Melatos, Badri Krishnan, John T. Whelan

Date: 23 Feb 2011

Abstract: A strategy is devised for a semi-coherent cross-correlation search for a young neutron star in the supernova remnant SNR 1987A, using science data from the Initial LIGO and/or Virgo detectors. An astrophysical model for the gravitational wave phase is introduced which describes the star's spin down in terms of its magnetic field strength $B$ and ellipticity $\epsilon$, instead of its frequency derivatives. The model accurately tracks the gravitational wave phase from a rapidly decelerating neutron star under the restrictive but computationally unavoidable assumption of constant braking index, an issue which has hindered previous searches for such young objects. The theoretical sensitivity is calculated and compared to the indirect, age-based wave strain upper limit. The age-based limit lies above the detection threshold in the frequency band 75\,Hz $\lesssim \nu \lesssim 450$\,Hz. The semi-coherent phase metric is also calculated and used to estimate the optimal search template spacing for the search. The range of search parameters that can be covered given our computational resources ($\sim 10ˆ9$ templates) is also estimated. For Initial LIGO sensitivity, in the frequency band between 50\,Hz and 500\,Hz, in the absence of a detected signal, we should be able to set limits of $B \gtrsim 10ˆ{11}$\,G and $\epsilon \lesssim 10ˆ{-4}$.

abs pdf

Feb 24, 2011

1102.4654 (/preprints)
2011-02-24, 15:38 [edit]


[1102.4614] Stellar mass black holes in star clusters: gravitational wave emission and detection rates

Authors: Sambaran Banerjee (AIfA, Bonn)

Date: 22 Feb 2011

Abstract: We investigate the dynamics of stellar-mass black holes (BH) in star clusters focusing on the dynamical formation of BH-BH binaries, which are very important sources of gravitational waves (GW). We examine the properties of these BH-BH binaries through direct N-body computations of Plummer clusters, having initially N(0) <= 10ˆ5 low mass stars and a population of stellar mass BHs, using the state-of-the-art N-body integrator "NBODY6". We find that the stellar mass BHs segregate rapidly into the cluster core to form a central dense sub-cluster of BHs in which BH-BH binaries form via 3-body encounters. While most of the BH binaries finally escape from the cluster by recoils due to super-elastic encounters with the single BHs, we find that for clusters with N(0) >= 5 X 10ˆ4, typically a few of them dynamically harden to the extent that they can merge via GW emission within the cluster. Also, for each of such clusters, there are a few escaped BH binaries that merge within a Hubble time, most of the mergers happening within a few Gyr of cluster evolution. These results imply that the intermediate-aged massive clusters constitute the most important class of star clusters that can produce dynamical BH-BH mergers at the present epoch. The BH-BH merger rates obtained from our computations imply a significant detection rate (~ 30/yr) for the "Advanced LIGO" GW detector that will become operative in the near future. Finally, we briefly discuss our ongoing development on this work incorporating the formation of BHs in star clusters from stellar evolution. In particular, we highlight the effect of stellar metallicity on the BH sub-cluster driven expansion of a star cluster's core.

abs pdf

Feb 24, 2011

1102.4614 (/preprints)
2011-02-24, 15:38 [edit]


[1102.4824] Pulsar Timing Sensitivities to Gravitational Waves from Relativistic Metric Theories of Gravity

Authors: Marcio Eduardo da Silva Alves, Massimo Tinto

Date: 23 Feb 2011

Abstract: Pulsar timing experiments aimed at the detection of gravitational radiation have been performed for decades now. With the forthcoming construction of large arrays capable of tracking multiple millisecond pulsars, it is very likely we will be able to make the first detection of gravitational radiation in the nano-Hertz band, and test Einstein's theory of relativity by measuring the polarization components of the detected signals. Since a gravitational wave predicted by the most general relativistic metric theory of gravity accounts for {\it six} polarization modes (the usual two Einstein's tensor polarizations as well as two vector and two scalar wave components), we have estimated the single-antenna sensitivities to these six polarizations. We find pulsar timing experiments to be significantly more sensitive, over their entire observational frequency band ($\approx 10ˆ{-9} - 10ˆ{-6}$ Hz), to scalar-longitudinal and vector waves than to scalar-transverse and tensor waves. At $10ˆ{-7}$ Hz and with pulsars at a distance of $1$ kpc, for instance, we estimate an average sensitivity to scalar-longitudinal waves that is more than two orders of magnitude better than the sensitivity to tensor waves. Our results imply that a direct detection of gravitational radiation by pulsar timing will result into a test of the theory of general relativity that is more stringent than that based on monitoring the decay of the orbital period of a binary system.

abs pdf

Feb 24, 2011

1102.4824 (/preprints)
2011-02-24, 15:38 [edit]


[1102.4362] Equivalence Principle and Gravitational Redshift

Authors: Michael A. Hohensee, Steven Chu, Achim Peters, Holger Mueller

Date: 21 Feb 2011

Abstract: We investigate leading order deviations from general relativity that violate the Einstein equivalence principle (EEP) in the gravitational standard model extension (SME). We show that redshift experiments based on matter waves and clock comparisons are equivalent to one another. Consideration of torsion balance tests, along with matter wave, microwave, optical, and M\"ossbauer clock tests yields comprehensive limits on spin-independent EEP-violating SME terms at the $10ˆ{-6}$ level.

abs pdf

Feb 23, 2011

1102.4362 (/preprints)
2011-02-23, 13:48 [edit]


[1102.4348] Cosmic recycling of millisecond pulsars

Authors: Wynn C. G. Ho, Thomas J. Maccarone, Nils Andersson (University of Southampton)

Date: 21 Feb 2011

Abstract: We compare the rotation rate of neutron stars in low-mass X-ray binaries (LMXBs) with the orbital period of the binaries. We find that, while short orbital period LMXBs span a range of neutron star rotation rates, all the long period LMXBs have fast rotators. We also find that the rotation rates are highest for the systems with the highest mean mass accretion rates, as can be expected if the accretion rate correlates with the orbital period. We show that these properties can be understood by a balance between spin-up due to accretion and spin-down due to gravitational radiation. Our scenario indicates that the gravitational radiation emitted by these systems may be detectable by future ground-based gravitational wave detectors.

abs pdf

Feb 23, 2011

1102.4348 (/preprints)
2011-02-23, 13:48 [edit]


[1102.3706] Bumpy Black Holes in Alternate Theories of Gravity

Authors: Sarah Vigeland, Nicol&#xe1;s Yunes, Leo Stein

Date: 17 Feb 2011

Abstract: We generalize the bumpy black hole framework to allow for alternative theory deformations. We construct two model-independent parametric deviations from the Kerr metric: one built from a generalization of the quasi-Kerr and bumpy metrics and one built directly from perturbations of the Kerr spacetime in Lewis-Papapetrou form. We find the conditions that these "bumps" must satisfy for there to exist an approximate second-order Killing tensor so that the perturbed spacetime still possesses three constants of the motion (a deformed energy, angular momentum and Carter constant) and the geodesic equations can be written in first-order form. We map these parameterized metrics to each other via a diffeomorphism and to known analytical black hole solutions in alternative theories of gravity. The parameterized metrics presented here serve as frameworks for the systematic calculation of extreme-mass ratio inspiral waveforms in parameterized non-GR theories and the investigation of the accuracy to which space-borne gravitational wave detectors can constrain such deviations.

abs pdf

Feb 20, 2011

1102.3706 (/preprints)
2011-02-20, 18:36 [edit]


[1102.3781] Search for gravitational waves from binary black hole inspiral, merger and ringdown

Authors: The LIGO Scientific Collaboration, the Virgo Collaboration

Date: 18 Feb 2011

Abstract: We present the first modeled search for gravitational waves using the complete binary black hole gravitational waveform from inspiral through the merger and ringdown for binaries with negligible component spin. We searched approximately 2 years of LIGO data taken between November 2005 and September 2007 for systems with component masses of 1-99 solar masses and total masses of 25-100 solar masses. We did not detect any plausible gravitational-wave signals but we do place upper limits on the merger rate of binary black holes as a function of the component masses in this range. We constrain the rate of mergers for binary black hole systems with component masses between 19 and 28 solar masses and negligible spin to be no more than 2.0 per Mpcˆ3 per Myr at 90% confidence.

abs pdf

Feb 20, 2011

1102.3781 (/preprints)
2011-02-20, 18:36 [edit]


[1102.3647] Gravitational Waves Notes, Issue #5 : "The Capra research programme for capture of small compact objects by massive black holes"

Authors: Pau Amaro-Seoane, Bernard Schutz, Jonathan Thornburg

Date: 17 Feb 2011

Abstract: GW Notes was born from the need for a journal where the distinct communities involved in gravitation wave research might gather. While these three communities - astrophysics, general relativity and data analysis - have made significant collaborative progress over recent years, we believe that it is indispensable to future advancement that they draw closer, and that they speak a common idiom. In this 6th GW Note (since we started numbering with #0), we present the work of Jonathan Thornburg, who has been fully-refereed, on the Capra research programme for capture of small compact objects by massive black holes.

abs pdf

Feb 20, 2011

1102.3647 (/preprints)
2011-02-20, 10:29 [edit]


[1102.3612] Violations of Einstein's Relativity: Motivations, Theory, and Phenomenology

Authors: Ralf Lehnert

Date: 17 Feb 2011

Abstract: One of the most difficult questions in present-day physics concerns a fundamental theory of space, time, and matter that incorporates a consistent quantum description of gravity. There are various theoretical approaches to such a quantum-gravity theory. Nevertheless, experimental progress is hampered in this research field because many models predict deviations from established physics that are suppressed by some power of the Planck scale, which currently appears to be immeasurably small. However, tests of relativity theory provide one promising avenue to overcome this phenomenological obstacle: many models for underlying physics can accommodate a small breakdown of Lorentz symmetry, and numerous feasible Lorentz-symmetry tests have Planck reach. Such mild violations of Einstein's relativity have therefore become a focus of recent research efforts. This presentation provides a brief survey of the key ideas in this research field and is geared at both experimentalists and theorists. In particular, several theoretical mechanisms leading to deviations from relativity theory are presented; the standard theoretical framework for relativity violations at currently accessible energy scales (i.e., the SME) is reviewed, and various present and near-future experimental efforts within this field are discussed.

abs pdf

Feb 20, 2011

1102.3612 (/preprints)
2011-02-20, 10:28 [edit]


[1102.3434] Detecting Vanishing Dimensions Via Primordial Gravitational Wave Astronomy

Authors: Jonas R. Mureika, Dejan Stojkovic

Date: 16 Feb 2011

Abstract: Lower-dimensionality at higher energies has manifold theoretical advantages as recently pointed out. Moreover, it appears that experimental evidence may already exists for it - a statistically significant planar alignment of events with energies higher than TeV has been observed in some earlier cosmic ray experiments. We propose a robust and independent test for this new paradigm. Since (2+1)-dimensional spacetimes have no gravitational degrees of freedom, gravity waves cannot be produced in that epoch. This places a universal maximum frequency at which primordial waves can propagate, marked by the transition between dimensions. We show that this cut-off frequency may be accessible to future gravitational wave detectors such as LISA.

abs pdf

Feb 20, 2011

1102.3434 (/preprints)
2011-02-20, 10:28 [edit]


[1102.3355] Gravitational Wave Detection by Interferometry (Ground and Space)

Authors: Matthew Pitkin, Stuart Reid, Sheila Rowan, Jim Hough

Date: 16 Feb 2011

Abstract: 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.

abs pdf

Feb 16, 2011

1102.3355 (/preprints)
2011-02-16, 21:37 [edit]


[1102.3180] Stellar Dynamics of Extreme-Mass-Ratio Inspirals

Authors: David Merritt, Tal Alexander, Seppo Mikkola, Clifford Will

Date: 15 Feb 2011

Abstract: Inspiral of compact stellar remnants into massive black holes (MBHs) is accompanied by the emission of gravitational waves at frequencies that are potentially detectable by the proposed laser interferometer space antenna. Event rates computed from statistical (Fokker-Planck, Monte-Carlo) approaches span a wide range due to uncertaintities about the rate coefficients. Here we present results from direct integration of the post-Newtonian N-body equations of motion descrbing dense clusters of compact stars around Schwarzschild and Kerr MBHs. These simulations embody an essentially exact (at the post-Newtonian level) treatment of the interplay between stellar dynamical relaxation, relativistic precession, and gravitational-wave energy loss. The rate of capture of stars by the MBH is found to be greatly reduced by relativistic precession, which limits the ability of torques from the stellar potential to change orbital angular momenta. Penetration of this "Schwarzschild barrier" does occasionally occur, resulting in capture of stars onto orbits that gradually inspiral due to gravitational wave emission; we discuss two mechanisms for barrier penetration and find evidence for both in the simulations. We derive an approximate formula for the capture rate, which predicts that captures would be strongly disfavored from orbits with semi-major axes below a certain value; this prediction, as well as the predicted rate, are verified in the N-body integrations. Adding spin to the MBH does not substantially change the capture rate; the back-reaction of the stellar torques on the spin of the MBH is evaluated and shown to be potentially observable. We discuss the implications of our results for the detection of extreme-mass-ratio inspirals from galactic nuclei with a range of physical properties.

abs pdf

Feb 16, 2011

1102.3180 (/preprints)
2011-02-16, 14:54 [edit]


[1102.2857] The Capra Research Program for Modelling Extreme Mass Ratio Inspirals

Authors: Jonathan Thornburg

Date: 14 Feb 2011

Abstract: Suppose a small compact object (black hole or neutron star) of mass $m$ orbits a large black hole of mass $M \gg m$. This system emits gravitational waves (GWs) that have a radiation-reaction effect on the particle's motion. EMRIs (extreme--mass-ratio inspirals) of this type will be important GW sources for LISA; LISA's data analysis will require highly accurate EMRI GW templates. In this article I outline the "Capra" research program to try to model EMRIs and calculate their GWs \textit{ab initio}, assuming only that $m \ll M$ and that the Einstein equations hold. Here we treat the EMRI spacetime as a perturbation of the large black hole's "background" (Schwarzschild or Kerr) spacetime and use the methods of black-hole perturbation theory, expanding in the small parameter $m/M$. The small body's motion can be described either as the result of a radiation-reaction "self-force" acting in the background spacetime or as geodesic motion in a perturbed spacetime. Several different lines of reasoning lead to the (same) basic $\O(m/M)$ "MiSaTaQuWa" equations of motion for the particle. Surprisingly, for a nonlinear field theory such as general relativity, modelling the small body as a point particle works well. The particle's own field is singular along the particle worldline so it's difficult to formulate a meaningful "perturbation" theory or equations of motion there. I discuss "mode-sum" and "puncture-function" regularization schemes that resolve this difficulty and allow practical self-force calculations, and I outline an important recent calculation of this type.
Most Capra research to date has used 1st order perturbation theory. To obtain the very high accuracies needed to fully exploit LISA's observations of the strongest EMRIs, 2nd order perturbation theory will probably be needed.

abs pdf

Feb 15, 2011

1102.2857 (/preprints)
2011-02-15, 17:28 [edit]


[1102.2230] On detection of the stochastic gravitational-wave background using the Parkes pulsar timing array

Authors: D. R. B. Yardley, W. A. Coles, G. B. Hobbs, J. P. W. Verbiest, R. N. Manchester, W. van Straten, F. A. Jenet, M. Bailes, N. D. R. Bhat, S. Burke-Spolaor, D. J. Champion, A. W. Hotan, S. Oslowski, J. E. Reynolds, J. M. Sarkissian

Date: 10 Feb 2011

Abstract: We search for the signature of an isotropic stochastic gravitational-wave background in pulsar timing observations using a frequency-domain correlation technique. These observations, which span roughly 12 yr, were obtained with the 64-m Parkes radio telescope augmented by public domain observations from the Arecibo Observatory. A wide range of signal processing issues unique to pulsar timing and not previously presented in the literature are discussed. These include the effects of quadratic removal, irregular sampling, and variable errors which exacerbate the spectral leakage inherent in estimating the steep red spectrum of the gravitational-wave background. These observations are found to be consistent with the null hypothesis, that no gravitational-wave background is present, with 76 percent confidence. We show that the detection statistic is dominated by the contributions of only a few pulsars because of the inhomogeneity of this data set. The issues of detecting the signature of a gravitational-wave background with future observations are discussed.

abs pdf

Feb 13, 2011

1102.2230 (/preprints)
2011-02-13, 23:10 [edit]


[1102.2001] Elementary analysis of the special relativistic combination of velocities, Wigner rotation, and Thomas precession

Authors: Kane O&#x27;Donnell (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)

Date: 9 Feb 2011

Abstract: The purpose of this paper is to provide an elementary introduction to the qualitative and quantitative results of velocity combination in special relativity, including the Wigner rotation and Thomas precession. We utilize only the most familiar tools of special relativity, in arguments presented at three differing levels: (1) utterly elementary, which will suit a first course in relativity; (2) intermediate, to suit a second course; and (3) advanced, to suit higher level students. We then give a summary of useful results, and suggest further reading in this often obscure field.

abs pdf

Feb 10, 2011

1102.2001 (/preprints)
2011-02-10, 22:19 [edit]


[1102.1749] On the use of higher order waveforms in the search for gravitational waves emitted by compact binary coalescences

Authors: D. J. A. McKechan

Date: 8 Feb 2011

Abstract: This thesis concerns the use, in gravitational wave data analysis, of higher order waveform models of the gravitational radiation emitted by compact binary coalescences. We begin with an introductory chapter that includes an overview of the theory of general relativity, gravitational radiation and ground-based interferometric gravitational wave detectors. We then discuss, in Chapter 2, the gravitational waves emitted by compact binary coalescences, with an explanation of higher order waveforms and how they differ from leading order waveforms; we also introduce the post-Newtonian formalism. In Chapter 3 the method and results of a gravitational wave search for low mass compact binary coalescences using a subset of LIGO's 5th science run data are presented and in the subsequent chapter we examine how one could use higher order waveforms in such analyses. We follow the development of a new search algorithm that incorporates higher order waveforms with promising results for detection efficiency and parameter estimation. In Chapter 5, a new method of windowing time-domain waveforms that offers benefit to gravitational wave searches is presented. The final chapter covers the development of a game designed as an outreach project to raise public awareness and understanding of the search for gravitational waves.

abs pdf

Feb 10, 2011

1102.1749 (/preprints)
2011-02-10, 09:28 [edit]


[1102.0769] Constraining the dark energy equation of state using LISA observations of spinning Massive Black Hole binaries

Authors: Antoine Petiteau, Stanislav Babak, Alberto Sesana

Date: 3 Feb 2011

Abstract: Gravitational wave signals from coalescing Massive Black Hole (MBH) binaries could be used as standard sirens to measure cosmological parameters. The future space based gravitational wave observatory Laser Interferometer Space Antenna (LISA) will detect up to a hundred of those events, providing very accurate measurements of their luminosity distances. To constrain the cosmological parameters we also need to measure the redshift of the galaxy (or cluster of galaxies) hosting the merger. This requires the identification of a distinctive electromagnetic event associated to the binary coalescence. However, putative electromagnetic signatures may be too weak to be observed. Instead, we study here the possibility of constraining the cosmological parameters by enforcing statistical consistency between all the possible hosts detected within the measurement error box of a few dozen of low redshift (z<3) events. We construct MBH populations using merger tree realizations of the dark matter hierarchy in a LambdaCDM Universe, and we use data from the Millennium simulation to model the galaxy distribution in the LISA error box. We show that, assuming that all the other cosmological parameters are known, the parameter w describing the dark energy equation of state can be constrained to a 4-8% level (2sigma error), competitive with current uncertainties obtained by type Ia supernovae measurements, providing an independent test of our cosmological model.

abs pdf

Feb 09, 2011

1102.0769 (/preprints)
2011-02-09, 12:00 [edit]


[1102.1020] Radio Remnants of Compact Binary Mergers - the Electromagnetic Signal that will follow the Gravitational Waves

Authors: Ehud Nakar, Tsvi Piran

Date: 4 Feb 2011

Abstract: The question "what is the observable electromagnetic (EM) signature of a compact binary merger?" is an intriguing one with crucial consequences to the quest for gravitational waves (GW). Compact binary mergers are prime sources of GW, targeted by current and next generation detectors. Numerical simulations have demonstrated that these mergers eject energetic sub-relativistic (or even relativistic) outflows. This is certainly the case if the mergers produce short GRBs, but even if not, significant outflows are expected. The interaction of such outflows with the surround matter inevitably leads to a long lasting radio signal. We calculate the expected signal from these outflows (our calculations are also applicable to short GRB orphan afterglows) and we discuss their detectability. We show that the optimal search for such signal should, conveniently, take place around 1.4 GHz. Realistic estimates of the outflow parameters yield signals of a few hundred $\mu$Jy, lasting a few weeks, from sources at the detection horizon of advanced GW detectors. Followup radio observations, triggered by GW detection, could reveal the radio remnant even under unfavorable conditions. Upcoming all sky surveys can detect a few dozen, and possibly even thousands, merger remnants at any give time, thereby providing robust merger rate estimates even before the advanced GW detectors become operational. In fact, the radio transient RT 19870422 fits well the overall properties predicted by our model and we suggest that its most probable origin is a compact binary merger radio remnant.

abs pdf

Feb 09, 2011

1102.1020 (/preprints)
2011-02-09, 11:59 [edit]


[1102.0327] Growing Massive Black Holes in a Local Group Environment: the Central Supermassive, Slowly Sinking, and Ejected Populations

Authors: Miroslav Micic, Kelly Holley-Bockelmann, Steinn Sigurdsson

Date: 2 Feb 2011

Abstract: We explore the growth of < 10ˆ7 Msun black holes that reside at the centers of spiral and field dwarf galaxies in a Local Group type of environment. We use merger trees from a cosmological N-body simulation known as Via Lactea II (VL-2) as a framework to test two merger-driven semi-analytic recipes for black hole growth that include dynamical friction, tidal stripping, and gravitational wave recoil in over 20,000 merger tree realizations. First, we apply a Fundamental Plane limited (FPL) model to the growth of Sgr A*, which drives the central black hole to a maximum mass limited by the Black Hole Fundamental Plane after every merger. Next, we present a new model that allows for low-level Prolonged Gas Accretion (PGA) during the merger. We find that both models can generate a Sgr A* mass black hole. We predict a population of massive black holes in local field dwarf galaxies - if the VL-2 simulation is representative of the growth of the Local Group, we predict up to 35 massive black holes (< 10ˆ6 Msun) in Local Group field dwarfs. We also predict that hundreds of < 10ˆ5 Msun black holes fail to merge, and instead populate the Milky Way halo, with the most massive of them at roughly the virial radius. In addition, we find that there may be hundreds of massive black holes ejected from their hosts into the nearby intergalactic medium due to gravitational wave recoil. We discuss how the black hole population in the Local Group field dwarfs may help to constrain the growth mechanism for Sgr A*.

abs pdf

Feb 03, 2011

1102.0327 (/preprints)
2011-02-03, 12:34 [edit]


[1102.0262] Physics of Coevolution of Galaxies and Supermassive Black Holes

Authors: Renyue Cen (Princeton University Observatory)

Date: 1 Feb 2011

Abstract: A model for coevolution of galaxies and supermassive black holes (SMBH) is presented that is physically based. The starting point is a gas-rich major merger that triggers a starburst and the endpoint is a quiescent elliptical galaxy many gigayears later. There is an approximate coevolution between starburst galaxies and elliptical galaxies, although it is not exact in several important ways. Starburst precedes the onset of main SMBH growth with a gap of time equal to ~100Myr and is responsible for shutting down its own activities; AGN has little to do with it. While starburst occurs earlier and lasts for only about 100Myrs, the AGN accretion occurs later and lasts for ~1 Gyr or longer with a diminishing Eddington ratio. The main AGN growth in post-starburst phase is fueled by recycled gas from inner bulge stars and self-regulated. The predicted relation between SMBH mass and bulge mass/velocity dispersion is consistent with observations. A suite of testable and falsifiable predictions and implications with respect to relationships between various types of galaxies and AGN are made. Where comparisons to extant observations are possible, the model is in agreement with them.

abs pdf

Feb 03, 2011

1102.0262 (/preprints)
2011-02-03, 12:33 [edit]


Preprints and articles of interest

Feb 02, 2011

home (/preprints)
2011-02-02, 18:37 [edit]


  Login:   Password:   [rss] [cc] [w3] [css]

© M. Vallisneri 2012 — last modified on 2010/01/29

Tantum in modicis, quantum in maximis