[1108.4421] Intermediate-mass-ratio black hole binaries II: Modeling Trajectories and Gravitational Waveforms

Authors: Hiroyuki Nakano, Yosef Zlochower, Carlos O. Lousto, Manuela Campanelli

Date: 22 Aug 2011

Abstract: We revisit the scenario of small-mass-ratio (q) black-hole binaries; performing new, more accurate, simulations of mass ratios 10:1 and 100:1 for initially nonspinning black holes. We propose fitting functions for the trajectories of the two black holes as a function of time and mass ratio (in the range 1/100 < q < 1/10$) that combine aspects of post-Newtonian trajectories at smaller orbital frequencies and plunging geodesics at larger frequencies. We then use these trajectories to compute waveforms via black hole perturbation theory. Using the advanced LIGO noise curve, we see a match of ~99.5% for the leading (l,m)=(2,2) mode between the numerical relativity and perturbative waveforms. Nonleading modes have similarly high matches. We thus prove the feasibility of efficiently generating a bank of gravitational waveforms in the intermediate-mass-ratio regime using only a sparse set of full numerical simulations.

abs pdf

Aug 24, 2011

1108.4421 (/preprints)
2011-08-24, 21:47 [edit]


[1108.4485] Stability and chaos of hierarchical three black hole configurations

Authors: Pablo Galaviz

Date: 23 Aug 2011

Abstract: We study the stability and chaos of three compact objects using post-Newtonian (PN) equations of motion derived from the Arnowitt-Deser-Misner-Hamiltonian formulation, where we include terms up to 2.5 PN order in the orbital part and the leading order in spin corrections. We perform numerical simulations of a hierarchical configuration of three compact bodies in which a binary system is perturbed by a third, lighter body initially far away from the binary. The relative importance of the different PN orders is examined. The basin boundary method and the computation of Lyapunov exponent are employed to analyze the stability and chaotic properties of the system. The 1 PN terms produce a small but noticeable change in the stability regions of the parameters considered. On the other hand, the inclusion of spin or gravitational radiation does not produce a significant change with respect to the inclusion of the 1 PN terms.

abs pdf

Aug 24, 2011

1108.4485 (/preprints)
2011-08-24, 21:47 [edit]


[1108.4740] The final stages of accretion onto non-Kerr compact objects

Authors: Cosimo Bambi, Enrico Barausse

Date: 24 Aug 2011

Abstract: The $5 - 20 M_\odot$ dark objects in X-ray binary systems and the $10ˆ5 - 10ˆ9 M_\odot$ dark objects in galactic nuclei are currently thought to be the Kerr black holes predicted by General Relativity. However, direct observational evidence for this identification is still elusive, and the only viable approach to confirm the Kerr black hole hypothesis is to explore and rule out any other possibility. Here we investigate the final stages of the accretion process onto generic compact objects. While for Kerr black holes and for more oblate bodies the accreting gas reaches the innermost stable circular orbit (ISCO) and plunges into the compact object, we find that for more prolate bodies several scenarios are possible, depending on the spacetime geometry. In particular, we find examples in which the gas reaches the ISCO, but then gets trapped between the ISCO and the compact object. In this situation, accretion onto the compact object is possible only if the gas loses additional angular momentum, forming torus-like structures inside the ISCO.

abs pdf

Aug 24, 2011

1108.4740 (/preprints)
2011-08-24, 21:30 [edit]


[1108.3121] The gravitational-wave memory from eccentric binaries

Authors: Marc Favata

Date: 15 Aug 2011

Abstract: The nonlinear gravitational-wave memory causes a time-varying but nonoscillatory correction to the gravitational-wave polarizations. It arises from gravitational-waves that are sourced by gravitational-waves. Previous considerations of the nonlinear memory effect have focused on quasicircular binaries. Here I consider the nonlinear memory from Newtonian orbits with arbitrary eccentricity. Expressions for the waveform polarizations and spin-weighted spherical-harmonic modes are derived for elliptic, hyperbolic, parabolic, and radial orbits. In the hyperbolic, parabolic, and radial cases the nonlinear memory provides a 2.5 post-Newtonian (PN) correction to the leading-order waveforms. This is in contrast to the elliptical and quasicircular cases, where the nonlinear memory corrects the waveform at leading (0PN) order. This difference in PN order arises from the fact that the memory builds up over a short "scattering" timescale in the hyperbolic case, as opposed to a much longer radiation-reaction timescale in the elliptical case. The nonlinear memory corrections presented here complete our knowledge of the leading-order (Peters-Mathews) waveforms for elliptical orbits. These calculations are also relevant for binaries with quasicircular orbits in the present epoch which had, in the past, large eccentricities. Because the nonlinear memory depends sensitively on the past evolution of a binary, I discuss the effect of this early-time eccentricity on the value of the late-time memory in nearly-circularized binaries. I also discuss the observability of large "memory jumps" in a binary's past that could arise from its formation in a capture process. Lastly, I provide estimates of the signal-to-noise ratio of the linear and nonlinear memories from hyperbolic and parabolic binaries.

abs pdf

Aug 16, 2011

1108.3121 (/preprints)
2011-08-16, 21:03 [edit]


[1108.3174] Towards low-latency real-time detection of gravitational waves from compact binary coalescences in the era of advanced detectors

Authors: Jing Luan (Caltech), Shaun Hooper (UWA), Linqing Wen (UWA), Yanbei Chen (Caltech)

Date: 16 Aug 2011

Abstract: Electromagnetic (EM) follow-up observations of gravitational wave (GW) events will help shed light on the nature of the sources, and more can be learned if the EM follow-ups can start as soon as the GW event becomes observable. In this paper, we propose a computationally efficient time-domain algorithm capable of detecting gravitational waves (GWs) from coalescing binaries of compact objects with nearly zero time delay. In case when the signal is strong enough, our algorithm also has the flexibility to trigger EM observation before the merger. The key to the efficiency of our algorithm arises from the use of chains of so-called Infinite Impulse Response (IIR) filters, which filter time-series data recursively. Computational cost is further reduced by a template interpolation technique that requires filtering to be done only for a much coarser template bank than otherwise required to sufficiently recover optimal signal-to-noise ratio. Towards future detectors with sensitivity extending to lower frequencies, our algorithm's computational cost is shown to increase rather insignificantly compared to the conventional time-domain correlation method. Moreover, at latencies of less than hundreds to thousands of seconds, this method is expected to be computationally more efficient than the straightforward frequency-domain method.

abs pdf

Aug 16, 2011

1108.3174 (/preprints)
2011-08-16, 21:03 [edit]


[1108.3110] Tidal Interactions in Merging White Dwarf Binaries

Authors: Anthony L. Piro (Caltech)

Date: 15 Aug 2011

Abstract: The recently discovered system J0651 is the tightest known detached white dwarf (WD) binary. Since it has not yet initiated Roche-lobe overflow, it provides a relatively clean environment for testing our understanding of tidal interactions. I investigate the tidal heating of each WD, parameterized in terms of its tidal Q parameter. Assuming that the heating can be radiated efficiently, the current luminosities are consistent with Q_1=7*10ˆ{10} and Q_2=2*10ˆ7, for the He and C/O WDs, respectively. Conversely, if the observed luminosities are merely from the cooling of the WDs, these estimated values of Q represent upper limits. A large Q_1 for the He WD means its spin velocity will be slower than that expected if it was tidally locked, which, since the binary is eclipsing, may be measurable via the Rossiter-McLaughlin effect. After one year, gravitational wave emission shifts the time of eclipses by 5.5 s, but tidal interactions cause the orbit to shrink more rapidly, changing the time by up to an additional 0.3 s after a year. Future eclipse timing measurements may therefore infer the degree of tidal locking.

abs pdf

Aug 16, 2011

1108.3110 (/preprints)
2011-08-16, 21:03 [edit]


[1108.3186] Summed Parallel Infinite Impulse Response (SPIIR) Filters For Low-Latency Gravitational Wave Detection

Authors: Shaun Hooper (UWA), Shin Kee Chung (UWA), Jing Luan (Caltech), David Blair (UWA), Yanbei Chen (Caltech), Linqing Wen (UWA)

Date: 16 Aug 2011

Abstract: With the upgrade of current gravitational wave detectors, the first detection of gravitational wave signals is expected to occur in the next decade. Low-latency gravitational wave triggers will be necessary to make fast follow-up electromagnetic observations of events related to their source, e.g., prompt optical emission associated with short gamma-ray bursts. In this paper we present a new time-domain low-latency algorithm for identifying the presence of gravitational waves produced by compact binary coalescence events in noisy detector data. Our method calculates the signal to noise ratio from the summation of a bank of parallel infinite impulse response (IIR) filters. We show that our summed parallel infinite impulse response (SPIIR) method can retrieve the signal to noise ratio to greater than 99% of that produced from the optimal matched filter. We emphasise the benefits of the SPIIR method for advanced detectors, which will require larger template banks.

abs pdf

Aug 16, 2011

1108.3186 (/preprints)
2011-08-16, 21:02 [edit]


[1108.3106] Testing Extended General Relativity with galactic sizes and compact gravitational sources

Authors: Mariano Anabitarte, Mat&#xed;as Reynoso, Pablo Alejandro S&#xe1;nchez, Jes&#xfa;s Mart&#xed;n Romero, Mauricio Bellini

Date: 15 Aug 2011

Abstract: Considering a five-dimensional (5D) Riemannian spacetime with a particular stationary Ricci-flat metric, we have applied the recently developed Extended General Relativistic theory to calculate the lower limit for the size of some relevant galaxies: the Milky Way, Andromeda and M87. Our results are in very good agreement with observations.

abs pdf

Aug 16, 2011

1108.3106 (/preprints)
2011-08-16, 21:00 [edit]


[1108.2638] Coalescence Rate of Supermassive Black Hole Binaries Derived from Cosmological Simulations: Detection Rates for LISA and ET

Authors: Ch. Filloux, J.A. de Freitas Pacheco, F. Durier, J.C.N. de Araujo

Date: 12 Aug 2011

Abstract: The coalescence history of massive black holes has been derived from cosmological simulations, in which the evolution of those objects and that of the host galaxies are followed in a consistent way. The present study indicates that supermassive black holes having masses greater than $\sim 10ˆ{9} M_{\odot}$ underwent up to 500 merger events along their history. The derived coalescence rate per comoving volume and per mass interval permitted to obtain an estimate of the expected detection rate distribution of gravitational wave signals ("ring-down") along frequencies accessible by the planned interferometers either in space (LISA) or in the ground (Einstein). For LISA, in its original configuration, a total detection rate of about $15 yrˆ{-1}$ is predicted for events having a signal-to-noise ratio equal to 10, expected to occur mainly in the frequency range $4-9 mHz$. For the Einstein gravitational wave telescope, one event each 14 months down to one event each 4 years is expected with a signal-to-noise ratio of 5, occurring mainly in the frequency interval $10-20 Hz$. The detection of these gravitational signals and their distribution in frequency would be in the future an important tool able to discriminate among different scenarios explaining the origin of supermassive black holes.

abs pdf

Aug 15, 2011

1108.2638 (/preprints)
2011-08-15, 08:17 [edit]


[1108.2700] It was twenty years ago today ...

Authors: Paul Ginsparg (Cornell University)

Date: 14 Aug 2011

Abstract: To mark the 20th anniversary of the (14 Aug 1991) commencement of hep-th@xxx.lanl.gov (now arXiv.org), I've adapted this article from one that first appeared in Physics World (2008), was later reprinted (with permission) in Learned Publishing (2009), but never appeared in arXiv. I trace some historical context and early development of the resource, its later trajectory, and close with some thoughts about the future.
This version is closer to my original draft, with some updates for this occasion, plus an astounding $2ˆ5$ added footnotes.

abs pdf

Aug 14, 2011

1108.2700 (/preprints)
2011-08-14, 23:41 [edit]


[1108.2375] Scalar-Tensor-Vector Gravity, Galaxy Rotation Curves, and Quadrupole Gravitational Polarization

Authors: Priti Mishra, T. P. Singh

Date: 11 Aug 2011

Abstract: The standard cold dark matter model is the best fit to cosmological observations and to galaxy rotation curves. However, unless there is a direct detection of dark matter, either in the laboratory or in astronomical observations, one should allow for modified gravity theories such as MOND or Scalar-Tensor-Vector Gravity as possible explanations for flatness of galaxy rotation curves. The STVG theory due to Moffat and collaborators modifies general relativity by the addition of a massive vector field, and the vector field coupling constant, its mass, and the gravitational constant, are dynamical scalar fields. The theory is shown to yield a modified acceleration law which has a repulsive Yukawa component added to the Newtonian law of gravitational acceleration, and which can explain the observed flatness of a large class of galaxy rotation curves by fixing the values of two free parameters [a mass scale and a length scale]. Here we provide a possible insight into the success of the STVG theory, by considering the effect of quadrupole polarization on the averaged gravitational field inside a galaxy, due to the pull of neighboring galaxies. This effect is analogous to the polarization induced modification of averaged electromagnetic fields in a medium, and was studied by Szekeres in the context of propagation of gravitational waves. The study was generalized to the case of a static weak-field approximation by Zalaletdinov and collaborators, who showed that the effect of quadrupole polarization is to modify Poisson's equation for the gravitational potential to a fourth order [biharmonic] equation. We show that, remarkably, the biharmonic equation implies a modified Newtonian acceleration which is of the same repulsive Yukawa form as in the STVG theory, and the corrections could in principle be large enough to explain flatness of the rotation curves.

abs pdf

Aug 13, 2011

1108.2375 (/preprints)
2011-08-13, 08:52 [edit]


[1108.2410] Application of asymptotic expansions for maximum likelihood estimators' errors to gravitational waves from binary mergers: the network case

Authors: Salvatore Vitale, Michele Zanolin

Date: 11 Aug 2011

Abstract: This paper describes the most accurate analytical frequentist assessment to date of the uncertainties in the estimation of physical parameters from gravitational waves generated by non spinning binary systems and Earth-based networks of laser interferometers. The paper quantifies how the accuracy in estimating the intrinsic parameters mostly depends on the network signal to noise ratio (SNR), but the resolution in the direction of arrival also strongly depends on the network geometry.
We compare results for 6 different existing and possible global networks and two different choices of the parameter space. We show how the fraction of the sky where the one sigma angular resolution is below 2 square degrees increases about 3 times when transitioning from the Hanford (USA), Livingston (USA) and Cascina (Italy) network to possible 5 sites ones (while keeping the network SNR fixed).
The technique adopted here is an asymptotic expansion of the uncertainties in inverse powers of the signal to noise ratio where the first order is the inverse Fisher information matrix. We show that a common approach to use simplified parameter spaces and only the Fisher information matrix can largely underestimate the uncertainties (by a factor ~7 for the one sigma sky uncertainty in square degrees at a network SNR of ~15).

abs pdf

Aug 13, 2011

1108.2410 (/preprints)
2011-08-13, 08:51 [edit]


[1108.1423] Scientific Potential of Einstein Telescope

Authors: B.Sathyaprakash, M.Abernathy, F.Acernese, P.Amaro-Seoane N.Andersson, K.Arun, F.Barone, B.Barr, M.Barsuglia, M.Beker N.Beveridge, S.Birindelli, S.Bose, L.Bosi, S.Braccini, C.Bradaschia, T.Bulik, E.Calloni, G.Cella, E.Chassande.Mottin, S.Chelkowski, A.Chincarini, J.Clark, E.Coccia, C.Colacino, J.Colas, A.Cumming, L.Cunningham, E.Cuoco, S.Danilishin, K.Danzmann, R.De.Salvo, T.Dent, R.De.Rosa, L.Di.Fiore, A.Di.Virgilio, M.Doets, V.Fafone, P.Falferi, R.Flaminio, J.Franc, F.Frasconi, A.Freise, D.Friedrich, P.Fulda, J.Gair, G.Gemme, E.Genin, A.Gennai, A.Giazotto, K.Glampedakis, C.Gr&#xe4;f, M.Granata, H.Grote, G.Guidi, A.Gurkovsky, G.Hammond, M.Hannam, J.Harms, D.Heinert, M.Hendry, I.Heng, E.Hennes, S.Hild, J.Hough, S.Husa, S.Huttner, G.Jones, F.Khalili, K.Kokeyama, K.Kokkotas, B.Krishnan, T.G.F.Li, M.Lorenzini, H.L&#xfc;ck, E.Majorana, I.Mandel, V.Mandic, M.Mantovani, I.Martin, C.Michel, Y.Minenkov, N.Morgado, S.Mosca, B.Mours, H.M&#xfc;ller--Ebhardt, P.Murray, R.Nawrodt, J.Nelson, R.Oshaughnessy, C.D.Ott, C.Palomba, A.Paoli, G.Parguez, A.Pasqualetti, R.Passaquieti, D.Passuello, L.Pinard, W.Plastino, R.Poggiani, P.Popolizio, M.Prato, M.Punturo, P.Puppo, D.Rabeling, I.Racz, P.Rapagnani, J.Read, T.Regimbau, H.Rehbein, S.Reid, L.Rezzolla, F.Ricci, F.Richard, A.Rocchi, S.Rowan, A.R&#xfc;diger, L.Santamar&#xed;a, B.Sassolas, R.Schnabe, C.Schwarz, P.Seidel, A.Sintes, K.Somiya, F.Speirits, K.Strain, S.Strigin, P.Sutton, S.Tarabrin, A.Th&#xfc;ring, J.van.den.Brand, M.van.Veggel, C.van.den.Broeck, A.Vecchio, J.Veitch, F.Vetrano, A.Vicere, S.Vyatchanin, B.Willke, G.Woan, K.Yamamoto

Date: 5 Aug 2011

Abstract: Einstein gravitational-wave Telescope (ET) is a design study funded by the European Commission to explore the technological challenges of and scientific benefits from building a third generation gravitational wave detector. The three-year study, which concluded earlier this year, has formulated the conceptual design of an observatory that can support the implementation of new technology for the next two to three decades. The goal of this talk is to introduce the audience to the overall aims and objectives of the project and to enumerate ET's potential to influence our understanding of fundamental physics, astrophysics and cosmology.

abs pdf

Aug 10, 2011

1108.1423 (/preprints)
2011-08-10, 09:07 [edit]


[1108.1819] Faster computation of adiabatic EMRIs using resonances

Authors: Rebecca Grossman, Janna Levin, Gabe Perez-Giz

Date: 8 Aug 2011

Abstract: Motivated by the prohibitive computational cost of producing adiabatic extreme mass ratio inspirals, we explain how a judicious use of resonant orbits can dramatically expedite both that calculation and the generation of snapshot gravitational waves from geodesic sources. In the course of our argument, we clarify the resolution of a lingering debate on the appropriate adiabatic averaging prescription in favor of torus averaging over time averaging.

abs pdf

Aug 10, 2011

1108.1819 (/preprints)
2011-08-10, 09:06 [edit]


[1108.1826] Testing General Relativity with LISA including Spin Precession and Higher Harmonics in the Waveform

Authors: C&#xe9;dric Huwyler, Antoine Klein, Philippe Jetzer

Date: 8 Aug 2011

Abstract: In this paper, we compute the accuracy at which the planned space-based gravitational wave detector LISA will be able to observe deviations from General Relativity. To do so, we introduce six correction parameters that account for modified gravity in the second post-Newtonian gravitational wave phase for inspiralling supermassive black hole binaries with spin precession on quasi-circular orbits. The precession of the spins and the angular momentum modulate the gravitational waveform, resulting in additional structure which could reduce correlations in the parameter space and increase the detection accuracy of the alternative theory parameters. Also, the use of higher harmonics could create further structure and increase the time during which the signal lasts in the frequency window of LISA. In order to find error distributions for the alternative theory parameters, we use the Fisher information formalism and carry out Monte Carlo simulations for 17 different binary black hole mass configurations in the range 10ˆ5 Msun < M < 10ˆ8 Msun with 10ˆ3 randomly distributed points in the parameter space each, using the full (FWF) and restricted (RWF) version of the gravitational waveform. We find that the binaries can roughly be separated into two groups: one with low (\precsim 10ˆ7 Msun) and one with high total masses (\succsim 10ˆ7 Msun). The RWF errors on the alternative theory parameters are two orders of magnitude higher than the FWF errors for high-mass binaries while almost comparable for low-mass binaries. Due to dilution of the available information, the accuracy of the binary parameters is reduced by factors of a few, except for the luminosity distance which is affected more seriously in the high-mass regime. As an application, we compute an optimal lower bound on the graviton mass which is increased by a factor of ~1.5 when using the FWF.

abs pdf

Aug 10, 2011

1108.1826 (/preprints)
2011-08-10, 09:06 [edit]


[1108.1317] Precision measurement of the Hubble constant using gravitational waves

Authors: Walter Del Pozzo

Date: 5 Aug 2011

Abstract: The precise measurement of the Hubble constant $H_0$ is one of the foundations of the current cosmological paradigm. Due to correlations between $H_0$ and the remaining cosmological parameters, a precise measurement of $H_0$ is critical in view of future high redshift surveys. Second generation ground-based laser interferometers are expected to deliver a wealth of gravitational waves (GW) events from coalescing compact binaries up to a redshift of about 0.3. Being free of the systematics affecting electromagnetic measurements, GW offer the possibility of an independent measurement of $H_0$ with great accuracy. This \emph{Letter} presents a general method based on Bayesian inference aimed at estimating the value of the cosmological parameters for any GW event. In contrast to earlier work, this framework does not require the precise identification of the putative optical counterpart, but it considers all the potential galaxy hosts consistent with the recovered sky position and distance posterior distributions. When applied to the worldwide network of second generation interferometers, 50 GW events will yield a measurement of $H_0$ with an uncertainty of few percent.

abs pdf

Aug 08, 2011

1108.1317 (/preprints)
2011-08-08, 09:17 [edit]


[1108.1307] Gravitational waves from compact binaries

Authors: Marc van der Sluys

Date: 5 Aug 2011

Abstract: In this review, I give a summary of the history of our understanding of gravitational waves and how compact binaries were used to transform their status from mathematical artefact to physical reality. I also describe the types of compact (stellar) binaries that LISA will observe as soon as it is switched on. Finally, the status and near future of LIGO, Virgo and GEO are discussed, as well as the expected detection rates for the Advanced detectors, and the accuracies with which binary parameters can be determined when BH/NS inspirals are detected.

abs pdf

Aug 08, 2011

1108.1307 (/preprints)
2011-08-08, 09:17 [edit]


[1108.1189] Gravitational waves from spinning black hole-neutron star binaries: dependence on black hole spins and on neutron star equations of state

Authors: Koutarou Kyutoku, Hirotada Okawa, Masaru Shibata, Keisuke Taniguchi

Date: 4 Aug 2011

Abstract: We study the merger of black hole (BH)-neutron star (NS) binaries with a variety of BH spins aligned or anti-aligned with the orbital angular momentum, and with the mass ratio in the range MBH/MNS = 2--5, where MBH and MNS are the mass of the BH and NS, respectively. We model NS matter by systematically parametrized piecewise polytropic equations of state. The initial condition is computed in the puncture framework adopting an isolated horizon framework to estimate the BH spin and assuming an irrotational velocity field for the fluid inside the NS. Dynamical simulations are performed in full general relativity by an adaptive mesh refinement code, SACRA. The treatment of hydrodynamic equations and estimation of the disk mass are improved. We find that the NS is tidally disrupted irrespective of the mass ratio when the BH has a moderately large prograde spin, whereas only binaries with low mass ratios, MBH/MNS <~ 3 or small compactnesses of the NSs, bring the tidal disruption when the BH spin is zero or retrograde. The mass of the remnant disk is accordingly large as >~ 0.1 Msun, which is required by central engines of short gamma-ray bursts, if the BH spin is prograde. Information of the tidal disruption is reflected in a clear relation between the compactness of the NS and an appropriately defined "cutoff frequency" in the gravitational-wave spectrum, above which the spectrum damps exponentially. We find that the tidal disruption of the NS and excitation of the quasinormal mode of the remnant BH occur in a compatible manner in high mass-ratio binaries with the prograde BH spin. The correlation between the compactness and the cutoff frequency still holds for such cases. It is also suggested by extrapolation that the merger of an extremely spinning BH and an irrotational NS binary does not lead to formation of an overspinning BH.

abs pdf

Aug 08, 2011

1108.1189 (/preprints)
2011-08-08, 09:16 [edit]


[gr-qc/0509116] FINDCHIRP: an algorithm for detection of gravitational waves from inspiraling compact binaries

Authors: Bruce Allen, Warren G. Anderson, Patrick R. Brady, Duncan A. Brown, Jolien D. E. Creighton

Date: 28 Sep 2005

Abstract: Matched-filter searches for gravitational waves from coalescing compact binaries by the LIGO Scientific Collaboration use the findchirp algorithm: an implementation of the optimal filter with innovations to account for unknown signal parameters and to improve performance on detector data that has non-stationary and non-Gaussian artifacts. We provide details on the methods used in the findchirp algorithm as used in the search for sub-solar mass binaries, binary neutron stars, neutron star--black hole binaries and binary black holes.

abs pdf

Aug 05, 2011

0509116 (/preprints/gr-qc)
2011-08-05, 13:01 [edit]


[1108.1163] Dynamical Friction around Supermassive Black Holes

Authors: Fabio Antonini, David Merritt

Date: 4 Aug 2011

Abstract: The density of stars in galactic bulges is often observed to be flat or slowly rising inside the influence radius of the supermassive black hole (SMBH). Chandrasekhar's dynamical friction formula predicts little or no frictional force on a test body in such a core, regardless of its density, due to the absence of stars moving more slowly than the local circular velocity. We have tested this prediction using large-scale $N$-body experiments. The rate of orbital decay never drops precisely to zero, because stars moving faster than the test body also contribute to the frictional force. When the contribution from the fast-moving stars is included in the expression for the dynamical friction force, and the changes induced by the massive body on the stellar distribution are taken into account, Chandrasekhar's theory is found to reproduce the rate of orbital decay remarkably well. However, this rate is still substantially smaller than the rate predicted by Chandrasekhar's formula in its most widely-used forms, implying longer time scales for inspiral. Motivated by recent observations that suggest a parsec-scale core around the Galactic center SMBH, we investigate the evolution of a population of stellar-mass black holes (BHs) as they spiral in to the center of the Galaxy. After $\sim 10$ Gyr, we find that the density of BHs can remain substantially less than the density in stars at all radii; we conclude that it would be unjustified to assume that the spatial distribution of BHs at the Galactic center is well described by steady-state models. One consequence is that rates of capture of BHs by the SMBH at the Galactic center (EMRIs) may be much lower than in standard models. When capture occurs, inspiraling BHs often reach the gravitational-radiation-dominated regime while on orbits that are still highly eccentric.

abs pdf

Aug 05, 2011

1108.1163 (/preprints)
2011-08-05, 13:01 [edit]


[1108.0995] Constructing EOB dynamics with numerical energy flux for intermediate-mass-ratio inspirals

Authors: Wen-Biao Han, Zhoujian Cao

Date: 4 Aug 2011

Abstract: A new scheme for computing dynamical evolutions and gravitational radiations for intermediate-mass-ratio inspirals (IMRIs) based on an effective one-body (EOB) dynamics plus Teukolsky perturbation theory is built in this paper. In the EOB framework, the dynamics essentially affects the resulted gravitational waveform for binary compact star system. This dynamics includes two parts. One is the conservative part which comes from effective one-body reduction. The other part is the gravitational back reaction which contributes to the shrinking process of the inspiral of binary compact star system. Previous works used analytical waveform to construct this back reaction term. Since the analytical form is based on post-Newtonian expansion, the consistency of this term is always checked by numerical energy flux. Here we directly use numerical energy flux by solving the Teukolsky equation via the frequency-domain method to construct this back reaction term. And the conservative correction to the leading order terms in mass-ratio is included in the deformed-Kerr metric and the EOB Hamiltonian. We try to use this method to simulate not only quasi-circular adiabatic inspiral but also the nonadiabatic plunge phase. For several different spinning black holes, we demonstrate and compare the resulted dynamical evolutions and gravitational waveforms.

abs pdf

Aug 05, 2011

1108.0995 (/preprints)
2011-08-05, 13:00 [edit]


[1108.0812] High signal-to-noise ratio observations and the ultimate limits of precision pulsar timing

Authors: Stefan Oslowski, Willem van Straten, George Hobbs, Matthew Bailes, Paul Demorest

Date: 3 Aug 2011

Abstract: We demonstrate that the sensitivity of high-precision pulsar timing experiments will be ultimately limited by the broadband intensity modulation that is intrinsic to the pulsar's stochastic radio signal. That is, as the peak flux of the pulsar approaches that of the system equivalent flux density, neither greater antenna gain nor increased instrumental bandwidth will improve timing precision. These conclusions proceed from an analysis of the covariance matrix used to characterise residual pulse profile fluctuations following the template matching procedure for arrival time estimation. We perform such an analysis on 25 hours of high-precision timing observations of the closest and brightest millisecond pulsar, PSR J0437-4715. In these data, the standard deviation of the post-fit arrival time residuals is approximately four times greater than that predicted by considering the system equivalent flux density, mean pulsar flux and the effective width of the pulsed emission. We develop a technique based on principal component analysis to mitigate the effects of shape variations on arrival time estimation and demonstrate its validity using a number of illustrative simulations. When applied to our observations, the method reduces arrival time residual noise by approximately 20%. We conclude that, owing primarily to the intrinsic variability of the radio emission from PSR J0437-4715 at 20 cm, timing precision in this observing band better than 30 - 40 ns in one hour is highly unlikely, regardless of future improvements in antenna gain or instrumental bandwidth. We describe the intrinsic variability of the pulsar signal as stochastic wideband impulse modulated self-noise (SWIMS) and argue that SWIMS will likely limit the timing precision of every millisecond pulsar currently observed by Pulsar Timing Array projects as larger and more sensitive antennae are built in the coming decades.

abs pdf

Aug 03, 2011

1108.0812 (/preprints)
2011-08-03, 23:42 [edit]


[1107.3585] Model-Independent Comparisons of Pulsar Timings to Scalar-Tensor Gravity

Authors: M.W. Horbatsch, C.P. Burgess

Date: 18 Jul 2011

Abstract: Observations of pulsar timing provide strong constraints on scalar-tensor theories of gravity, but these constraints are traditionally quoted as limits on the microscopic parameters (like the Brans-Dicke coupling, for example) that govern the strength of scalar-matter couplings at the particle level in particular models. Here we present fits to timing data for several pulsars directly in terms of the phenomenological couplings (masses, scalar charges, moments of inertia and so on) of the stars involved, rather than to the more microscopic parameters of a specific model. For instance, for the double pulsar PSR J0737-3039A/B we find with 95% confidence that m_A = (1.30 +/- 0.04)m_sun, m_B = (1.21 +/- 0.04)m_sun, while the scalar-charge to mass ratios satisfy |a_A| < 0.25, |a_B| < 0.25 and |a_B - a_A| < 0.0022. These constraints are independent of the details of the scalar tensor model involved, and of assumptions about the stellar equations of state. Our fits can be used to constrain a broad class of scalar tensor theories by computing the fit quantities as functions of the microscopic parameters in any particular model, reproducing in particular standard constraints when applied to Brans-Dicke and quasi-Brans-Dicke models.

abs pdf

Aug 02, 2011

1107.3585 (/preprints)
2011-08-02, 23:28 [edit]


[1108.0205] Galactic foreground contributions to the WMAP5 maps

Authors: N. Macellari (1), E. Pierpaoli (1), C. Dickinson (2), J. Vaillancourt (3) ((1) USC, (2) JBCA, University of Manchester, (3) Caltech)

Date: 31 Jul 2011

Abstract: We compute the cross correlation of the intensity and polarisation from the 5-year WMAP data in different sky-regions with respect to template maps for synchrotron, dust, and free-free emission. We derive the frequency dependence and polarisation fraction for all three components in 48 different sky regions of HEALPix (Nside=2) pixelisation. The anomalous emission associated with dust is clearly detected in intensity over the entire sky at the K (23 GHz) and Ka (33 GHz) WMAP bands, and is found to be the dominant foreground at low Galactic latitude, between b=-40 and b=+10. The synchrotron spectral index obtained from the K and Ka WMAP bands from an all-sky analysis is -3.32\pm 0.12 for intensity and -3.01\pm0.03 for the polarised intensity. The polarisation fraction of the synchrotron is constant in frequency and increases with latitude from ~5% near the Galactic plane up to ~40% in some regions at high latitude; the average value for |b|<20 is 8.6\pm1.7 (stat) \pm0.5 (sys) % while for |b|>20 it is 19.3\pm0.8 (stat) \pm 0.5 (sys) %. Anomalous dust and free-free emission appear to be relatively unpolarised…[Abridged]…the average polarisation fraction of dust-correlated emission at K-band is 3.2\pm0.9 (stat) \pm 1.5 (sys) %, or less than 5% at 95% confidence. When comparing real data with simulations, 8 regions show a detected polarisation above the 99th percentile of the distribution from simulations with no input foreground polarisation, 6 of which are detected at above 2sigma and display polarisation fractions between 2.6% and 7.2%, except for one anomalous region, which has 32\pm12%. The dust polarisation values are consistent with the expectation from spinning-dust emission, but polarised dust emission from magnetic-dipole radiation cannot be ruled out. Free-free emission was found to be unpolarised with an upper limit of 3.4% at 95% confidence.

abs pdf

Aug 02, 2011

1108.0205 (/preprints)
2011-08-02, 07:41 [edit]


[1108.0302] What the information paradox is {\it not}

Authors: Samir D. Mathur

Date: 1 Aug 2011

Abstract: There still exist many confusions about the black hole information paradox and its resolution. We first give a precise formulation of the paradox, in four steps A-D. Then we examine several proposals for resolving the paradox. We note that in each case one of these four steps has been ignored, so that the proposal does not really target the essence of the paradox. Finally, we give a brief summary of the fuzzball construction and argue that it resolves the paradox in string theory. This resolution contains a deep lesson -- the phase space of quantum gravity is so large that the measure in the path integral can compete with the classical action for macroscopic objects undergoing gravitational collapse.

abs pdf

Aug 02, 2011

1108.0302 (/preprints)
2011-08-02, 07:41 [edit]


[1107.5809] Second-generation microlensing planet surveys: a realistic simulation

Authors: Yossi Shvartzvald, Dan Maoz

Date: 28 Jul 2011

Abstract: Microlensing surveys, which have discovered about a dozen extrasolar planets to date, have focused on the small minority of high-magnification lensing events, which have a high sensitivity to planet detection. In contrast, second-generation experiments, of the type that has recently begun, monitor continuously also the majority of low-magnification events. We carry out a realistic numerical simulation of such experiments. We simulate scaled, solar-like, eight-planet systems, studying a variety of physical parameters (planet frequency, scaling of the snowline with stellar mass R_snow ~ Mˆs), and folding in the various observational parameters (cadence, experiment duration), with sampling sequences and photometric error distributions taken from the real ongoing experiment. We quantify the dependence of detected planet yield on cadence and experiment duration, e.g., the yield is doubled when going from 3-hour to 15-minute baseline cadences, or from an 80-day-long to a 150-day-long experiment. There is a degeneracy between the snowline scaling index s and the abundance of planetary systems that can be inferred from the experiment. After 4 years, the ongoing second-generation experiment will discover of the order of 50 planets, and thus will be able to determine the frequency of snowline planet occurrence to 10-30% accuracy, assuming the fraction of stars hosting such planets is between 1/3 and 1/10, and a snowline index in the range s=0.5 to 2. If most planetary systems are solar analogs, over 65% of the detected planets will be "Jupiters", five in six of the detected anomalies will be due to a single planet, and one in six will reveal two planets in a single lensing event.

abs pdf

Aug 01, 2011

1107.5809 (/preprints)
2011-08-01, 06:42 [edit]


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