Bulletin of the American Physical Society
APS April Meeting 2012
Volume 57, Number 3
Saturday–Tuesday, March 31–April 3 2012; Atlanta, Georgia
Session C8: Gravitational-Wave Source Modeling |
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Sponsoring Units: GGR Chair: Bernard Kelly, University of Maryland Baltimore County Room: Embassy B |
Saturday, March 31, 2012 1:30PM - 1:42PM |
C8.00001: Accounting for Ringdown Mode-Mixing in Black-Hole Merger Waveforms Bernard Kelly, John Baker With rapid progress in numerical relativity recent years, the merger of comparable-mass black-hole binaries has become a reliable source of gravitational waveforms. The dominant harmonic modes $(l,m) = (2,\pm 2)$ are readily extracted and agree across research groups to high precision, making them suitable as raw material for high-accuracy template construction. However, examination of leading subdominant gravitational harmonic modes has revealed more complex behavior that impedes full modeling. For example, the $(3,\pm 2)$ mode, usually comparable to the $(4,4)$ in power content near merger, shows a complex frequency oscillation after merger, when the system should be ringing down to a Kerr end-state with constant quasi-normal mode (QNM) frequencies. Analysis indicates some kind of mode-mixing between the nominal $(3,2)$ mode and the dominant $(2,2)$ mode. We discuss the possible sources of this mode-mixing in numerical wave-extraction algorithms, and how to mitigate it to produce better-behaved waveforms that can be used for parameter estimation in gravitational-wave data analysis. [Preview Abstract] |
Saturday, March 31, 2012 1:42PM - 1:54PM |
C8.00002: A Subtlety with the Demodulation of Waveforms from Precessing Binaries Robert Owen, Michael Boyle, Harald Pfeiffer When compact objects in a binary system have generic spin directions, the orbital plane of the system precesses. This precession imparts an amplitude modulation on the spherical harmonic components of the gravitational radiation. To simplify waveform extrapolation and data analysis, several groups have recently proposed demodulation procedures that essentially amount to measuring the radiation in a coordinate frame that precesses along with the orbital plane. Unfortunately, because the space of asymptotic coordinate frames has higher dimension than the space of plane orientations, an extraneous degree of freedom arises in any such procedure. If this extra degree of freedom is fixed in a nongeometric way, the demodulated waveform can be corrupted by unphysical information, such as the choice of inertial asymptotic coordinate frame. I will discuss the geometry of the problem in some detail, and outline a physically-motivated criterion that fixes this degree of freedom, and therefore the demodulated waveform, uniquely. [Preview Abstract] |
Saturday, March 31, 2012 1:54PM - 2:06PM |
C8.00003: Reduced Basis representations of multi-mode black hole ringdown gravitational waves Scott Field, Sarah Caudill, Chad Galley, Frank Herrmann, Manuel Tiglio We construct compact and high accuracy Reduced Basis (RB) representations of single and multiple quasinormal modes. The RB method determines a hierarchical and relatively small set of the most relevant waveforms. We find that the exponential convergence of the method allows for a dramatic compression. Inclusion of a second mode is expected to help with detection, and might make it possible to infer details of the progenitor of the final black hole. We find, for example, that the number of RB waveforms needed to represent any two-mode ringdown waveform with an accuracy of $\sim 10^{-10}$ is {\em smaller} than the number of metric-based, one-mode templates with $MMm=0.99$. For unconstrained two-modes, which would allow for consistency tests of General Relativity, our high accuracy RB has around $10^4$ {\em fewer} waveforms than the number of metric-based templates for $MMm=0.99$. The number of RB elements grows only linearly with the number of multipole modes versus exponentially with the standard approach, resulting in very compact representations even for many multiple modes. These results open the possibility of searches of multi-mode ringdown gravitational waves. [Preview Abstract] |
Saturday, March 31, 2012 2:06PM - 2:18PM |
C8.00004: The Suitability of Hybrid Waveforms for Advanced Gravitational Wave Detectors Ilana MacDonald, Samaya Nissanke, Harald Pfeiffer Detectors such as Advanced LIGO are expected to measure gravitational wave (GW) signals from compact binaries within the next few years. In order to be able to characterize this type of signal, these detectors require accurate waveform models, which can be constructed by fusing an analytical post-Newtonian (PN) inspiral waveform with a numerical relativity (NR) late-inspiral-merger-ringdown waveform. NR, though the most accurate model, is computationally expensive: the longest simulations to date taking several months to run. PN theory, an analytic approximation to General Relativity, is easy to compute but becomes increasingly inaccurate near merger. Because of this trade-off, it is important to determine the optimal length of the NR waveform, while maintaining the necessary accuracy for GW detectors. We present a study of the sufficient accuracy of PN and NR waveforms for the most demanding usage case: parameter estimation of strong sources in advanced gravitational wave detectors. We perform a comprehensive analysis of errors that enter such ``hybrid waveforms'' in the case of equal- and unequal-mass non-spinning binaries. [Preview Abstract] |
Saturday, March 31, 2012 2:18PM - 2:30PM |
C8.00005: Gravitational waves from eccentric binary systems Valentin Necula, Sergey Klimenko, Guenakh Mitselmakher, Janna Levin Searches for compact binaries in general assume the standard formation mechanism, however such systems may also appear through dynamical interactions in the presence of supermassive black holes presumed to exist at the center of galaxies. These binaries are expected to have high initial eccentricities and the emitted gravitational radiation may enter the frequency range of ground-based detectors soon after they are formed, in contrast to standard compact binaries which circularize long before the merger time. A significant fraction of these binary systems may maintain high eccentricities throughout their lifetime, providing unique gravitational wave signatures which are not captured efficiently by searches designed for circular systems. We discuss this promising source of gravitational wave radiation and outline detection strategies with the initial and advanced ground-based detectors. [Preview Abstract] |
Saturday, March 31, 2012 2:30PM - 2:42PM |
C8.00006: EMRI gravitational waveforms including orbit--integrated self force effects Kristen Lackeos, Gaurav Khanna, Lior M. Burko We calculate the gravitational waveforms emitted from extreme mass ratio binaries for quasi-circular Schwarzschild orbits. The self force we use is the fully relativistic Barack--Sago self force for exact circular geodesics, which we use as an approximation. We calculate the emitted gravitational waveforms in two steps: first, we integrate the orbit, and then we use the obtained orbit to source the gravitational radiation by solving the inhomogeneous Teukolsky equation. The orbit is obtained by two independent methods: first, by direct integration of the ``relativistic second law'' --- 4-acceleration equals the self force per unit mass, and second by using the osculating orbits method. The (small) disagreement between the two methods serves as a measure of the systematic error. We compare our results also with the energy balance approach (neglecting conservative self force effects while keeping the dissipative effects). For the choice of mass ratio $10^{-2}$ starting at $10M$ down to $6.2M$ we find that the total dephasing effect associated with the conservative piece of the self force is $8.5\pm 0.4$ rad. Neglecting such a dephasing effect would reduce cross correlation integrals of data streaming with theoretical waveform and reduce the accuracy of parameter estimation. [Preview Abstract] |
Saturday, March 31, 2012 2:42PM - 2:54PM |
C8.00007: Maximum elastic deformations of relativistic stars Nathan Johnson-McDaniel, Benjamin Owen Deformed neutron stars are a prominent potential source of gravitational waves, and there are active searches for waves from such sources by the LIGO/Virgo collaboration. It is thus of considerable interest to know the maximum deformation that could be obtained for various models of neutron stars. We present here the first general relativistic calculations of such maximum quadrupoles in the case of elastic deformations. We consider the standard case of the quadrupoles generated by crustal deformations, and the somewhat more speculative case of quadrupoles generated by deformations of the hadron-quark mixed phase in hybrid stars, where we use our recent calculation of the shear modulus. In both cases, we find relativistic suppressions of the maximum quadrupole, compared with the standard, Newtonian calculations; these suppressions can be as large as a factor of 6 for the crustal quadrupoles of massive, compact stars. But even with these suppressions, maximally strained hybrid stars can still sustain quadrupoles large enough that they could have been detected in recent LIGO/Virgo searches (assuming that the large breaking strain recently calculated for the crust is applicable to the mixed phase in the core). [Preview Abstract] |
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