**Authors**: Matthew C. Johnson, Hiranya V. Peiris, Luis Lehner

**Date**: 19 Dec 2011

**Abstract**: Cosmic bubble collisions provide an important possible observational window on the dynamics of eternal inflation. In eternal inflation, our observable universe is contained in one of many bubbles formed from an inflating metastable vacuum. The collision between bubbles can leave a detectable imprint on the cosmic microwave background radiation. Although phenomenological models of the observational signature have been proposed, to make the theory fully predictive one must determine the bubble collision spacetime, and thus the cosmological observables, from a scalar field theory giving rise to eternal inflation. Because of the intrinsically non-linear nature of the bubbles and their collision, this requires a numerical treatment incorporating General Relativity. In this paper, we present results from numerical simulations of bubble collisions in full General Relativity. These simulations allow us to accurately determine the outcome of bubble collisions, and examine their effect on the cosmology inside a bubble universe. We confirm the validity of a number of approximations used in previous analytic work, and identify qualitatively new features of bubble collision spacetimes. Both vacuum bubbles and bubbles containing a realistic inflationary cosmology are studied. We identify the constraints on the scalar field potential that must be satisfied in order to obtain collisions that are consistent with our observed cosmology, yet leave detectable signatures.

1112.4487
(/preprints)

2011-12-21, 11:32
**[edit]**

**Authors**: Xinyi Guo, Ann Esin, Rosanne Di Stefano, Jeffrey Taylor

**Date**: 20 Dec 2011

**Abstract**: Gravitational microlensing events provide a potentially powerful tool for the study of stellar populations. In particular, they can be used to discover and study a variety of binary systems. A large number of binary lenses have already been found by the microlensing surveys and a few of these systems show strong evidence of orbital motion on the timescale of the lensing event. We expect that more of such binary lenses will be detected in the future. For binaries whose orbital period is comparable to the event duration, the orbital motion can cause the lensing signal to deviate drastically from that of a static binary lens. The most striking property of such lightcurves is the presence of quasi-periodic features, produced as the source traverses the same regions in the rotating lens plane. These repeated features contain information about the orbital period of the lens. If this period can be extracted, a lot can be learned about the lensing system even without performing a time-consuming detailed lightcurve modeling. However, the relative transverse motion between the source and the lens significantly complicates the problem of period extraction. To resolve this difficulty, we present a modification to the standard Lomb-Scargle periodogram analysis. We test our method for four representative binary lens systems and demonstrate its efficiency in correctly extracting binary orbital periods.

1112.4608
(/preprints)

2011-12-21, 11:32
**[edit]**

**Authors**: J. C. N. de Araujo, O. D. Aguiar, M. E. S. Alves, M. Tinto

**Date**: 7 Dec 2011

**Abstract**: We analyze the sensitivities of a geostationary gravitational wave interferometer mission operating in the sub-Hertz band. Our proposed Earth-orbiting detector is expected to meet some of the Laser Interferometer Space Antenna (LISA) mission science goals in the lower part of its accessible frequency band ($10ˆ{-4} - 2 \times 10ˆ{-2}$ Hz), and to outperform them by a large margin in the higher-part of it ($2 \times 10ˆ{-2} - 10$ Hz). Since our proposed interferometer will be more sensitive than LISA to supermassive black holes (SMBHs) of masses smaller than $\sim 10ˆ{6}$ M$_{\odot}$, we will be able to more accurately probe scenarios that account for their formation.

1112.1565
(/preprints)

2011-12-20, 09:16
**[edit]**

**Authors**: Alpha Mastrano, Andrew Melatos

**Date**: 7 Dec 2011

**Abstract**: Recent calculations of the hydromagnetic deformation of a stratified, non-barotropic neutron star are generalized to describe objects with superconducting interiors, whose magnetic permeability \mu is much smaller than the vacuum value \mu_0. It is found that the star remains oblate if the poloidal magnetic field energy is \gtrsim 40% of total magnetic field energy, that the toroidal field is confined to a torus which shrinks as \mu decreases, and that the deformation is much larger (by a factor \sim \mu_0/\mu) than in a non-superconducting object. The results are applied to the latest direct and indirect upper limits on gravitational-wave emission from Laser Interferometer Gravitational Wave Observatory (LIGO) and radio pulse timing (spin-down) observations of 81 millisecond pulsars, to show how one can use these observations to infer the internal field strength. It is found that the indirect spin-down limits already imply astrophysically interesting constraints on the poloidal-toroidal field ratio and diamagnetic shielding factor (by which accretion reduces the observable external magnetic field, e.g. by burial). These constraints will improve following gravitational-wave detections, with implications for accretion-driven magnetic field evolution in recycled pulsars and the hydromagnetic stability of these objects' interiors.

1112.1542
(/preprints)

2011-12-20, 09:16
**[edit]**

**Authors**: V. Predoi, for the LIGO Scientific Collaboration, for the Virgo Collaboration, K. Hurley, for IPN

**Date**: 7 Dec 2011

**Abstract**: We outline the scientific motivation behind a search for gravitational waves associated with short gamma ray bursts detected by the InterPlanetary Network (IPN) during LIGO's fifth science run and Virgo's first science run. The IPN localisation of short gamma ray bursts is limited to extended error boxes of different shapes and sizes and a search on these error boxes poses a series of challenges for data analysis. We will discuss these challenges and outline the methods to optimise the search over these error boxes.

1112.1637
(/preprints)

2011-12-20, 09:16
**[edit]**

**Authors**: Carl L. Rodriguez, Ilya Mandel, Jonathan R. Gair

**Date**: 6 Dec 2011

**Abstract**: The detection of gravitational waves from the inspiral of a neutron star or stellar-mass black hole into an intermediate-mass black hole (IMBH) promises an entirely new look at strong-field gravitational physics. Gravitational waves from these intermediate-mass-ratio inspirals (IMRIs), systems with mass ratios from ~10:1 to ~100:1, may be detectable at rates of up to a few tens per year by Advanced LIGO/Virgo and will encode a signature of the central body's spacetime. Direct observation of the spacetime will allow us to use the "no-hair" theorem of general relativity to determine if the IMBH is a Kerr black hole (or some more exotic object, e.g. a boson star). Using modified post-Newtonian (pN) waveforms, we explore the prospects for constraining the central body's mass-quadrupole moment in the advanced-detector era. We use the Fisher information matrix to estimate the accuracy with which the parameters of the central body can be measured. We find that for favorable mass and spin combinations, the quadrupole moment of a non-Kerr central body can be measured to within a ~15% fractional error or better using 3.5 pN order waveforms; on the other hand, we find the accuracy decreases to ~100% fractional error using 2 pN waveforms, except for a narrow band of values of the best-fit non-Kerr quadrupole moment.

1112.1404
(/preprints)

2011-12-20, 09:15
**[edit]**

**Authors**: Chengjian Wu, Vuk Mandic, Tania Regimbau

**Date**: 8 Dec 2011

**Abstract**: Compact binary coalescences, such as binary neutron stars or black holes, are among the most promising candidate sources for the current and future terrestrial gravitational-wave detectors. While such sources are best searched using matched template techniques and chirp template banks, integrating chirp signals from binaries over the entire Universe also leads to a gravitational-wave background (GWB). In this paper we systematically scan the parameter space for the binary coalescence GWB models, taking into account uncertainties in the star formation rate and in the delay time between the formation and coalescence of the binary, and we compare the computed GWB to the sensitivities of the second and third generation gravitational-wave detector networks. We find that second generation detectors are likely to detect the binary coalescence GWB, while the third generation detectors will probe most of the available parameter space. The binary coalescence GWB will, in fact, be a foreground for the third-generation detectors, potentially masking the GWB background due to cosmological sources. Accessing the cosmological GWB with third generation detectors will therefore require identification and subtraction of all inspiral signals from all binaries in the detectors' frequency band.

1112.1898
(/preprints)

2011-12-20, 09:13
**[edit]**

**Authors**: Lluís Bel

**Date**: 8 Dec 2011

**Abstract**: I comment about the adequacy of the GPS to model a particularly defined synchronization in a rotating frame of reference described in a general relativistic framework.

1112.2202
(/preprints)

2011-12-20, 09:11
**[edit]**

**Authors**: K. Liu, N. Wex, M. Kramer, J. M. Cordes, T. J. W. Lazio

**Date**: 9 Dec 2011

**Abstract**: The discovery of radio pulsars in compact orbits around Sgr A* would allow an unprecedented and detailed investigation of the spacetime of the supermassive black hole. This paper shows that pulsar timing, including that of a single pulsar, has the potential to provide novel tests of general relativity, in particular its cosmic censorship conjecture and no-hair theorem for rotating black holes. These experiments can be performed by timing observations with 100 micro-second precision, achievable with the Square Kilometre Array for a normal pulsar at frequency above 15 GHz. Based on the standard pulsar timing technique, we develop a method that allows the determination of the mass, spin, and quadrupole moment of Sgr A*, and provides a consistent covariance analysis of the measurement errors. Furthermore, we test this method in detailed mock data simulations. It seems likely that only for orbital periods below ~0.3 yr is there the possibility of having negligible external perturbations. For such orbits we expect a ~10ˆ-3 test of the frame dragging and a ~10ˆ-2 test of the no-hair theorem within 5 years, if Sgr A* is spinning rapidly. Our method is also capable of identifying perturbations caused by distributed mass around Sgr A*, thus providing high confidence in these gravity tests. Our analysis is not affected by uncertainties in our knowledge of the distance to the Galactic center, R0. A combination of pulsar timing with the astrometric results of stellar orbits would greatly improve the measurement precision of R0.

1112.2151
(/preprints)

2011-12-20, 09:10
**[edit]**

**Authors**: David Falta, Robert Fisher

**Date**: 13 Dec 2011

**Abstract**: We demonstrate that the integrated gravitational wave signal of Type Ia supernovae (SNe Ia) in the single-degenerate channel out to cosmological distances gives rise to a continuous background to spaceborne gravitational wave detectors, including the Big Bang Observer (BBO) and Deci-Hertz Interferometer Gravitational wave Observatory (DECIGO) planned missions. This gravitational wave background from SNe Ia acts as a noise background in the frequency range 0.1 - 10 Hz, which heretofore was thought to be relatively free from astrophysical sources apart from neutron star binaries, and therefore a key window in which to study primordial gravitational waves generated by inflation. While inflationary energy scales of $\gtrsim 10ˆ{16}$ GeV yield inflationary gravitational wave backgrounds in excess of our range of predicted backgrounds, for lower energy scales of $\sim10ˆ{15}$ GeV, the inflationary gravitational wave background becomes comparable to the noise background from SNe Ia.

1112.2782
(/preprints)

2011-12-20, 09:08
**[edit]**

**Authors**: James Healy, Tanja Bode, Roland Haas, Enrique Pazos, Pablo Laguna, Deirdre M. Shoemaker, Nicolás Yunes

**Date**: 16 Dec 2011

**Abstract**: Gravitational wave observations will probe non-linear gravitational interactions and thus enable strong tests of Einstein's theory of general relativity. We present a numerical relativity study of the late inspiral and merger of binary black holes in scalar-tensor theories of gravity. We consider black hole binaries in an inhomogeneous scalar field, specifically binaries inside a scalar field bubble, in some cases with a potential. We calculate the emission of dipole radiation. We also show how these configurations trigger detectable differences between gravitational waves in scalar-tensor gravity and the corresponding waves in general relativity. We conclude that, barring an external mechanism to induce dynamics in the scalar field, scalar-tensor gravity binary black holes alone are not capable of awaking a dormant scalar field, and are thus observationally indistinguishable from their general relativistic counterparts.

1112.3928
(/preprints)

2011-12-20, 09:07
**[edit]**

**Authors**: Nicolas Yunes

**Date**: 16 Dec 2011

**Abstract**: The future detection of gravitational wave forces us to consider the many ways in which astrophysics, gravitational wave theory and fundamental theory will interact. In this paper, I summarize some recent work done to develop such an interface. In particular, I concentrate on how non-vacuum astrophysical environments can modify the gravitational wave signal emitted by compact binary inspirals, and whether signatures from the former are detectable by current and future gravitational wave detectors. I also describe the interface between gravitational wave modeling and fundamental theory, focusing on the status of the parameterized post-Einsteinian framework (a general framework to detect deviations away from General Relativity in future gravitational wave data) and its current data analysis implementation.

1112.3694
(/preprints)

2011-12-20, 09:06
**[edit]**

**Authors**: Stoytcho S. Yazadjiev, Daniela D. Doneva

**Date**: 19 Dec 2011

**Abstract**: In the present paper we study the oscillation spectrum of neutron stars containing both ordinary matter and dark energy in different proportions. Within the model we consider, the equilibrium configurations are numerically constructed and the results show that the properties of the mixed neuron-dark-energy star can differ significantly when the amount of dark energy in the stars is varied. The oscillations of the mixed neuron-dark-energy stars are studied in the Cowling approximation. As a result we find that the frequencies of the fundamental mode and the higher overtones are strongly affected by the dark energy content. This can be used in the future to detect the presence of dark energy in the neutron stars and to constrain the dark-energy models.

1112.4375
(/preprints)

2011-12-20, 09:05
**[edit]**

**Authors**: Cemsinan Deliduman, K. Y. Ekşi, Vildan Keleş

**Date**: 18 Dec 2011

**Abstract**: We study the structure of neutron stars in R+\beta Rˆ{\mu \nu} R_{\mu \nu} gravity model with perturbative method. We obtain mass-radius relations for six representative equations of state (EOSs). We find that deviations from the results of general relativity, comparable to the variations due to using different EoSs, are induced for |\beta| ~ 10ˆ11 cmˆ2. Some of the soft EoSs that are excluded within the framework of general relativity can be reconciled for certain values of \beta\ of this order with the 2 solar mass neutron star recently observed. For some of the EoSs we find that a new solution branch, which allows highly massive neutron stars, exists for values of \beta\ greater than a few 10ˆ11 cmˆ2. We find constraints on \beta\ for a variety of EoSs using the recent observational constraints on the mass-radius relation. The associated length scale \sqrt{\beta} ~ 10ˆ6 cm is of the order of the the typical radius of neutron stars, the probe used in this test. This implies that the true value of \beta\ is most likely much smaller than 10ˆ11 cmˆ2.

1112.4154
(/preprints)

2011-12-20, 09:05
**[edit]**

**Authors**: Benoit Famaey, Stacy McGaugh

**Date**: 16 Dec 2011

**Abstract**: A wealth of astronomical data indicate the presence of mass discrepancies in the Universe. The motions observed in a variety of classes of extragalactic systems exceed what can be explained by the mass visible in stars and gas. Either (i) there is a vast amount of unseen mass in some novel form - dark matter - or (ii) the data indicate a breakdown of our understanding of gravity on the relevant scales, or (iii) both. Here, we first review a few outstanding challenges for the dark matter interpretation of mass discrepancies in galaxies, purely based on observations and independently of any alternative theoretical framework. We then show that many of these puzzling observations can be summarized by one single scaling relation - Milgrom's law - involving an acceleration constant (or a characteristic surface density) of the order of the square-root of the cosmological constant in natural units. This relation can at present most easily be interpreted as the effect of a single universal force law resulting from a modification of Newtonian dynamics (MOND) on galactic scales. We exhaustively review the current observational successes and problems of this alternative paradigm at all astrophysical scales, and summarize the various theoretical attempts (TeVeS, GEA, BIMOND, and others) made to effectively embed this modification of Newtonian dynamics within a generally covariant theory of gravity.

1112.3960
(/preprints)

2011-12-20, 09:04
**[edit]**

**Authors**: Jérôme Carré, Edward K. Porter

**Date**: 14 Dec 2011

**Abstract**: The inspiral of two compact objects in gravitational wave astronomy is described by a post-Newtonian expansion in powers of $(v/c)$. In most cases, it is believed that the post-Newtonian expansion is asymptotically divergent. A standard technique for accelerating the convergence of a power series is to re-sum the series by means of a rational polynomial called a Padé approximation. If we liken this approximation to a matrix, the best convergence is achieved by staying close to a diagonal Padé approximation. This broadly presents two subsets of the approximation : a super-diagonal approximation $PˆM_N$ and a sub-diagonal approximation $P_MˆN$, where $M = N+\epsilon$, and $\epsilon$ takes the values of 0 or 1. Left as rational polynomials, the coefficients in both the numerator and denominator need to be re-calculated as the order of the initial power series approximation is increased. However, the sub-diagonal Padé approximant is computationally advantageous as it can be expressed in terms of a Gauss-like continued fraction. Once in this form, each coefficient in the continued fraction is uniquely determined at each order. This means that as we increase the order of approximation of the original power series, we now have only one new additional coefficient to calculate in the continued fraction. While it is possible to provide explicit expressions for the continued fraction coefficients, they rapidly become unwieldy at high orders of approximation. It is also possible to numerically calculate the coefficients by means of ratios of Hankel determinants. However, these determinants can be ill-conditioned and lead to numerical instabilities. In this article, we present a method for calculating the continued fraction coefficients at arbitrary orders of approximation.

1112.3222
(/preprints)

2011-12-16, 22:07
**[edit]**

**Authors**: Yuta Okada, Nobuyuki Kanda, Sanjeev Dhurandhar, Hideyuki Tagoshi, Hirotaka Takahashi

**Date**: 14 Dec 2011

**Abstract**: The cross-correlation search for gravitational wave, which is known as 'radiometry', has been previously applied to map of the gravitational wave stochastic background in the sky and also to target on gravitational wave from rotating neutron stars/pulsars. We consider the Virgo cluster where may be appear as ‘hot spot’ spanning few pixels in the sky in radiometry analysis. Our results show that sufficient signal to noise ratio can be accumulated with integration times of the order of a year. We also construct numerical simulation of radiometry analysis, assuming current constructing/upgrading ground-based detectors. Point spread function of the injected sources are confirmed by numerical test. Typical resolution of radiometry analysis is a few square degree which corresponds to several thousand pixels of sky mapping.

1112.3090
(/preprints)

2011-12-16, 22:07
**[edit]**

**Authors**: Nobuyuki Kanda, the LCGT collaboration

**Date**: 14 Dec 2011

**Abstract**: Gravitational wave is a propagation of space-time distortion, which is predicted by Einstein in general relativity. Strong gravitational waves will come from some drastic astronomical objects, e.g. coalescence of neutron star binaries, black holes, supernovae, rotating pulsars and pulsar glitches. Detection of the gravitational waves from these objects will open a new door of \textit{‘gravitational wave astronomy’}. Gravitational wave will be a probe to study the physics and astrophysics. To search these gravitational waves, large-scale laser interferometers will compose a global network of detectors. Advanced LIGO and advanced Virgo are upgrading from currents detectors. One of LIGO detector is considering to move Australia Site. IndIGO or Einstein Telescope are future plans. LCGT (Large-scale Cryogenic Gravitational wave Telescope) is now constructing in Japan with distinctive characters: cryogenic cooling mirror and underground site. We will present a design and a construction status of LCGT, and brief status of current gravitational wave detectors in the world. Network of these gravitational wave detectors will start in late 2016 or 2017, and may discover the gravitational waves. For example, these detectors will reach its search range for coalescence of neutron star binary is over 200 Mpc, and several or more events per year will be expected. Since most of gravitational wave events are from high-energy phenomenon of the astronomical objects, these might have counterpart evidences in electromagnetic radiation (visible light, X/gamma ray), neutrino, high energy particles or others. Thus, the mutual follow-up observations will give us more information of these objects.

1112.3092
(/preprints)

2011-12-16, 22:07
**[edit]**

**Authors**: Ioannis Kamaretsos

**Date**: 14 Dec 2011

**Abstract**: A perturbed black hole emits gravitational radiation, usually termed the ringdown signal, whose frequency and damping time depends on the mass and spin of the black hole. I investigate the case of a binary black hole merger resulting from two initially non-spinning black holes of various mass ratios, in quasi-circular orbits. The observed ringdown signal will be determined, among other things, by the black hole's spin-axis orientation with respect to Earth, its sky position and polarization angle - parameters which can take any values in a particular observation. I have carried out a statistical analysis of the effect of these variables, focusing on detection and measurement of the multimode ringdown signals using the reformulated European LISA mission, Next Gravitational-Wave Observatory, NGO, the third generation ground-based observatory, Einstein Telescope and the advanced era detector, aLIGO. To the extent possible I have discussed the effect of these results on plausible event rates, as well as astrophysical implications concerning the formation and growth of supermassive and intermediate mass black holes.

1112.3077
(/preprints)

2011-12-16, 22:06
**[edit]**

**Authors**: Nicolas Yunes, Paolo Pani, Vitor Cardoso

**Date**: 14 Dec 2011

**Abstract**: A stellar-mass compact object spiraling into a supermassive black hole, an extreme-mass-ratio inspiral (EMRI), is one of the targets of future gravitational-wave detectors and it offers a unique opportunity to test General Relativity (GR) in the strong-field. We study whether generic scalar-tensor (ST) theories can be further constrained with EMRIs. We show that in the EMRI limit, all such theories universally reduce to massive or massless Brans-Dicke theory and that black holes do not emit dipolar radiation to all orders in post-Newtonian (PN) theory. For massless theories, we calculate the scalar energy flux in the Teukolsky formalism to all orders in PN theory and fit it to a high-order PN expansion. We derive the PN ST corrections to the Fourier transform of the gravitational wave response and map it to the parameterized post-Einsteinian framework. We use the effective-one-body framework adapted to EMRIs to calculate the ST modifications to the gravitational waveform. We find that such corrections are smaller than those induced in the early inspiral of comparable-mass binaries, leading to projected bounds on the coupling that are worse than current Solar System ones. Brans-Dicke theory modifies the weak-field, with deviations in the energy flux that are largest at small velocities. For massive theories, superradiance can lead to resonances in the scalar energy flux that can lead to floating orbits outside the innermost stable circular orbit and that last until the supermassive black hole loses enough mass and spin-angular momentum. If such floating orbits occur in the frequency band of LISA, they would lead to a large dephasing (~1e6 rads), preventing detection with GR templates. A detection that is consistent with GR would then rule out floating resonances at frequencies lower than the lowest observed frequency, allowing for the strongest constraints yet on massive ST theories.

1112.3351
(/preprints)

2011-12-16, 22:06
**[edit]**

**Authors**: David M. Alexander (Durham), Ryan C. Hickox (Durham, Dartmouth)

**Date**: 8 Dec 2011

**Abstract**: Massive black holes (BHs) are at once exotic and yet ubiquitous, residing in the centers of massive galaxies in the local Universe. Recent years have seen remarkable advances in our understanding of how these BHs form and grow over cosmic time, during which they are revealed as active galactic nuclei (AGN). However, despite decades of research, we still lack a coherent picture of the physical drivers of BH growth, the connection between the growth of BHs and their host galaxies, the role of large-scale environment on the fueling of BHs, and the impact of BH-driven outflows on the growth of galaxies. In this paper we review our progress in addressing these key issues, motivated by the science presented at the "What Drives the Growth of Black Holes?" workshop held at Durham on 26th-29th July 2010, and discuss how these questions may be tackled with current and future facilities.

1112.1949
(/preprints)

2011-12-11, 22:58
**[edit]**

**Authors**: Alan J. Weinstein, for the LIGO Scientific Collaboration, for the Virgo Collaboration

**Date**: 5 Dec 2011

**Abstract**: With the advanced gravitational wave detectors coming on line in the next 5 years, we expect to make the first detections of gravitational waves from astrophysical sources, and study the properties of the waves themselves as tests of General Relativity. In addition, these gravitational waves will be powerful tools for the study of their astrophysical sources and source populations. They carry information that is quite complementary to what can be learned from electromagnetic or neutrino observations, probing the central gravitational engines that power the electromagnetic emissions. Preparations are being made to enable near-simultaneous observations of both gravitational wave and electromagnetic observations of transient sources, using low-latency search pipelines and rapid sky localization. We will review the many opportunities for multi-messenger astronomy and astrophysics with gravitational waves enabled by the advanced detectors, and the preparations that are being made to quickly and fully exploit them.

1112.1057
(/preprints)

2011-12-07, 17:59
**[edit]**

**Authors**: Laura Book, Marc Kamionkowski, Fabian Schmidt

**Date**: 2 Dec 2011

**Abstract**: Weak-gravitational-lensing distortions to the intensity pattern of 21-cm radiation from the dark ages can be decomposed geometrically into curl and curl-free components. Lensing by primordial gravitational waves induces a curl component, while the contribution from lensing by density fluctuations is strongly suppressed. Angular fluctuations in the 21-cm background extend to very small angular scales, and measurements at different frequencies probe different shells in redshift space. There is thus a huge trove of information with which to reconstruct the curl component of the lensing field, allowing tensor-to-scalar ratios conceivably as small as r ~ 10ˆ{-9} - far smaller than those currently accessible - to be probed.

1112.0567
(/preprints)

2011-12-07, 17:58
**[edit]**

**Authors**: Zachariah B. Etienne, Yuk Tung Liu, Vasileios Paschalidis, Stuart L. Shapiro

**Date**: 2 Dec 2011

**Abstract**: As a neutron star (NS) is tidally disrupted by a black hole (BH) companion at the end of a BH-NS binary inspiral, its magnetic fields will be stretched and amplified. If sufficiently strong, these magnetic fields may impact the gravitational waveforms, merger evolution and mass of the remnant disk. Formation of highly-collimated magnetic field lines in the disk+spinning BH remnant may launch relativistic jets, providing the engine for a short-hard GRB. We analyze this scenario through fully general relativistic, magnetohydrodynamic (GRMHD) BHNS simulations from inspiral through merger and disk formation. Different initial magnetic field configurations and strengths are chosen for the NS interior for both nonspinning and moderately spinning (a/M=0.75) BHs aligned with the orbital angular momentum. Only strong interior (Bmax~10ˆ17 G) initial magnetic fields in the NS significantly influence merger dynamics, enhancing the remnant disk mass by 100% and 40% in the nonspinning and spinning BH cases, respectively. However, detecting the imprint of even a strong magnetic field may be challenging for Advanced LIGO. Though there is no evidence of mass outflows or magnetic field collimation during the preliminary simulations we have performed, higher resolution, coupled with longer disk evolutions and different initial magnetic field configurations, may be required to definitively assess the possibility of BHNS binaries as short-hard GRB progenitors.

1112.0568
(/preprints)

2011-12-07, 17:58
**[edit]**

**Authors**: Ramesh Narayan, Jeffrey E. McClintock

**Date**: 2 Dec 2011

**Abstract**: We show that the 5-GHz radio flux of transient ballistic jets in black hole binaries correlates with the dimensionless black hole spin parameter a* estimated via the continuum-fitting method. The data suggest that jet power scales either as the square of a* or the square of the angular velocity of the horizon. This is the first direct evidence that jets may be powered by black hole spin energy. The observed correlation validates the continuum-fitting method of measuring spin. In addition, for those black holes that have well-sampled radio observations of ballistic jets, the correlation may be used to obtain rough estimates of their spins.

1112.0569
(/preprints)

2011-12-07, 17:58
**[edit]**

**Authors**: F. K. Liu (PKU), Dong Wang (PKU), Xian Chen (KIAA-PKU)

**Date**: 5 Dec 2011

**Abstract**: Numerical relativity simulations predict that coalescence of supermassive black hole (SMBH) binaries not only leads to a spin flip but also to a recoiling of the merger remnant SMBHs. In the literature, X-shaped radio sources are popularly suggested to be candidates for SMBH mergers with spin flip of jet-ejecting SMBHs. Here we investigate the spectral and spatial observational signatures of the recoiling SMBHs in radio sources undergoing black hole spin flip. Our results show that SMBHs in most spin-flip radio sources have mass ratio $q\ga 0.3$ with a minimum possible value $q_{\rm min} \simeq 0.05$. For major mergers, the remnant SMBHs can get a kick velocity as high as $2100 km sˆ{-1}$ in the direction within an angle $\la 40ˆ\circ$ relative to the spin axes of remnant SMBHs, implying that recoiling quasars are biased to be with high Doppler-shifted broad emission lines while recoiling radio galaxies are biased to large apparent spatial off-center displacements. We also calculate the distribution functions of line-of-sight velocity and apparent spatial off-center for spin-flip radio sources with different apparent jet reorientation angles. Our results show that the larger the apparent jet reorientation angle is, the larger the Doppler-shifting recoiling velocity and apparent spatial off-center displacement will be. We investigate the effects of recoiling velocity on the dust torus in spin-flip radio sources and suggest that recoiling of SMBHs would lead to "dust poor" AGNs. Finally, we collect a sample of 19 X-shaped radio objects and for each object give the probability of detecting the predicted signatures of recoiling SMBH.

1112.1081
(/preprints)

2011-12-07, 17:55
**[edit]**

**Authors**: H.Meyer (Bergische Universitaet Wuppertal), E.Lohrmann, S.Schubert (Universitaet Hamburg), W.Bartel, A.Glazov, B.Loehr, C.Niebuhr, E.Wuensch (DESY), L.Joensson (University of Lund), G.Kempf (Hamburgische Schiffbau-Versuchsanstalt)

**Date**: 2 Dec 2011

**Abstract**: Newton's Law of Gravitation has been tested at small values of the acceleration, down to a=10ˆ{-10} m/sˆ2, the approximate value of MOND's constant a_0. No deviations were found.

1112.0434
(/preprints)

2011-12-05, 17:34
**[edit]**

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

*Tantum in modicis, quantum in maximis*