Symmetric Mass Ratio Research Articles

Constraining Possible γ-Ray Burst Emission from GW230529 Using Swift-BAT and Fermi-GBM

GW230529 is the first compact binary coalescence detected by the LIGO–Virgo–KAGRA collaboration with at least one component mass confidently in the lower mass gap, corresponding to the range 3–5 M ⊙. If interpreted as a neutron star–black hole merger, this event has the most symmetric mass ratio detected so far and therefore has a relatively high probability of producing electromagnetic (EM) emission. However, no EM counterpart has been reported. At the merger time t 0, Swift-BAT and Fermi-GBM together covered 100% of the sky. Performing a targeted search in a time window [t 0 − 20 s, t 0 + 20 s], we report no detection by the Swift-BAT and Fermi-GBM instruments. Combining the position-dependent γ-ray flux upper limits and the gravitational-wave posterior distribution of luminosity distance, sky localization, and inclination angle of the binary, we derive constraints on the characteristic luminosity and structure of the jet possibly launched during the merger. Assuming a top-hat jet structure, we exclude at 90% credibility the presence of a jet that has at the same time an on-axis isotropic luminosity ≳1048 erg s−1 in the bolometric band 1 keV–10 MeV and a jet opening angle ≳15°. Similar constraints are derived by testing other assumptions about the jet structure profile. Excluding GRB 170817A, the luminosity upper limits derived here are below the luminosity of any GRB observed so far.

The NANOGrav 12.5 yr Data Set: A Computationally Efficient Eccentric Binary Search Pipeline and Constraints on an Eccentric Supermassive Binary Candidate in 3C 66B

The radio galaxy 3C 66B has been hypothesized to host a supermassive black hole binary (SMBHB) at its center based on electromagnetic observations. Its apparent 1.05 yr period and low redshift (∼0.02) make it an interesting testbed to search for low-frequency gravitational waves (GWs) using pulsar timing array (PTA) experiments. This source has been subjected to multiple searches for continuous GWs from a circular SMBHB, resulting in progressively more stringent constraints on its GW amplitude and chirp mass. In this paper, we develop a pipeline for performing Bayesian targeted searches for eccentric SMBHBs in PTA data sets, and test its efficacy by applying it to simulated data sets with varying injected signal strengths. We also search for a realistic eccentric SMBHB source in 3C 66B using the NANOGrav 12.5 yr data set employing PTA signal models containing Earth term-only as well as Earth+pulsar term contributions using this pipeline. Due to limitations in our PTA signal model, we get meaningful results only when the initial eccentricity e 0 < 0.5 and the symmetric mass ratio η > 0.1. We find no evidence for an eccentric SMBHB signal in our data, and therefore place 95% upper limits on the PTA signal amplitude of 88.1 ± 3.7 ns for the Earth term-only and 81.74 ± 0.86 ns for the Earth+pulsar term searches for e 0 < 0.5 and η > 0.1. Similar 95% upper limits on the chirp mass are (1.98 ± 0.05) × 109 and (1.81 ± 0.01) × 109 M ☉. These upper limits, while less stringent than those calculated from a circular binary search in the NANOGrav 12.5 yr data set, are consistent with the SMBHB model of 3C 66B developed from electromagnetic observations.

Multiband gravitational wave observations of stellar binary black holes at the low to middle and high frequencies

ABSTRACT The ground-based gravitational wave (GW) observatories discover a population of merging stellar binary black holes (BBHs), which are promising targets for multiband observations by the low-, middle-, and high-frequency GW detectors. In this paper, we investigate the multiband GW detections of BBHs and demonstrate the advantages of such observations in improving the localization and parameter estimates of the sources. We generate mock samples of BBHs by considering different formation models as well as the merger rate density constrained by the current observations (GWTC-3). We specifically consider the astrodynamical middle-frequency interferometer GW observatory (AMIGO) in the middle-frequency band and estimate that it may detect 21–91 BBHs with signal-to-noise ratio ϱ ≥ 8 in a 4-yr observation period. The multiband observations by the low-frequency detectors [Laser Interferometer Space Antenna (LISA) and Taiji] and AMIGO may detect 5–33 BBHs with ϱLT ≥ 5 and ϱAMI ≥ 5, which can evolve to the high-frequency band within 4 yr and can be detected by the Cosmic Explorer (CE) and Einstein Telescope (ET). The joint observations of LISA-Taiji-AMIGO-ET-CE may localize the majority of the detectable BBHs in sky areas of 7 × 10−7 to 2 × 10−3 deg2, which is improved by a factor of ∼120, ∼2.4 × 105, ∼1.8 × 104, or ∼1.2 × 104, comparing with those by only adopting CE-ET, AMIGO, LISA-Taiji, or LISA-Taiji-AMIGO. These joint observations can also lead to an improvement of the measurement precision of the chirp mass (symmetric mass ratio) by a factor of ∼5.5 × 104 (33), ∼16 (8), ∼120 (90), or ∼5 (5), comparing with those by CE-ET, AMIGO, LISA-Taiji, or LISA-Taiji-AMIGO.

Extreme mass-ratio binary black hole merger: Characteristics of the test-particle limit

We study binary black hole mergers in the extreme mass-ratio limit. We determine the energy, angular momentum, and linear momentum of the post-merger, remnant black hole. Unlike previous works, we perform our analysis directly in the test-particle limit by solving the Regge-Wheeler-Zerilli wave equation with a source that moves along a geodesic. We rely on the fact that toward the merger, small mass-ratio binary systems follow a quasiuniversal geodesic trajectory. This formalism captures the final premerger stages of small mass-ratio binaries and thus provides a straightforward universal description in a region inaccessible to numerical relativity simulations. We present a general waveform template that may be used in the search for gravitational wave bursts from small and intermediate mass-ratio binary systems. Finally, this formalism gives a formal proof that the recoil velocity is quadratic in the symmetric mass ratio $\nu$. Specifically, the velocity is given by $V/c\approx 0.0467 \nu^2$. This result is about $4\%$ larger than previously estimated. Most of this difference stems from the inclusion of higher multipoles in our calculation.

Detectability and parameter estimation of stellar origin black hole binaries with next generation gravitational wave detectors

We consider stellar-origin black hole binaries, which are among the main astrophysical sources for next generation gravitational wave (GW) detectors such as the Einstein Telescope (ET) and Cosmic Explorer (CE). Using population models calibrated with the most recent LIGO/Virgo results from O3b run, we show that ET and CE will be capable of detecting tens of thousands of such sources (and virtually all of those present in our past light cone up to zlesssim 0.7 for ET and zlesssim 1 for CE) with a signal-to-noise ratio up to several hundreds, irrespective of the detector design. When it comes to parameter estimation, we use a Fisher-matrix analysis to assess the impact of the design on the estimation of the intrinsic and extrinsic parameters. We find that the CE detector, consisting of two distinct L-shape interferometers, has better sky localization performance compared to ET in its triangular configuration. We also find that the network is typically capable of measuring the chirp mass, symmetric mass ratio and spins of the binary at order of 10^{-5}, 10^{-4} and 10^{-4} fractional error respectively. While the fractional errors for the extrinsic parameters are of order 10^{-2} for the sky localization, luminosity distance and inclination.

Toward a gravitational self-force-informed effective-one-body waveform model for nonprecessing, eccentric, large-mass-ratio inspirals

Building upon several recent advances in the development of effective-one-body models for spin-aligned eccentric binaries with individual masses $(m_1,m_2)$ we introduce a new EOB waveform model that aims at describing inspiralling binaries in the large mass-ratio regime, $m_1\gg m_2$. The model exploits the current state-of-the-art TEOBResumS-Dali model for eccentric binaries, but the standard EOB potentials $(A,\bar{D},Q)$, informed by Numerical Relativity (NR) simulations, are replaced with the corresponding functions that are linear in the symmetric mass ratio $\nu\equiv m_1 m_2/(m_1+m_2)^2$ taken at 8.5PN accuracy. To improve their strong-field behavior, these functions are: (i) suitably factorized and resummed using Pad\'e approximants and (ii) additionally effectively informed to state-of-the-art numerical results obtained by gravitational self-force theory (GSF). For simplicity, the spin-sector of the model is taken to be the one of TEOBResumS-Dali, though removing the NR-informed spin-orbit effective corrections. We propose the current GSF-informed EOB framework as a conceptually complete analytical tool to generate waveforms for eccentric Extreme (and Intermediate) Mass Ratio Inspirals for future gravitational wave detectors.

Redshift factor and the small mass-ratio limit in binary black hole simulations

We present a calculation of the Detweiler redshift factor in binary black hole simulations based on its relation to the surface gravity. The redshift factor has far-reaching applications in analytic approximations, gravitational self-force calculations, and conservative two-body dynamics. By specializing to nonspinning, quasicircular binaries with mass ratios ranging from ${m}_{A}/{m}_{B}=1$ to ${m}_{A}/{m}_{B}=9.5$ we are able to recover the leading small-mass-ratio (SMR) prediction with relative differences of order ${10}^{\ensuremath{-}5}$ from simulations alone. The next-to-leading order term that we extract agrees with the SMR prediction arising from self-force calculations, with differences of a few percent. These deviations from the first-order conservative prediction are consistent with nonadiabatic effects that can be accommodated in an SMR expansion. This fact is also supported by a comparison to the conservative post-Newtonian prediction of the redshifts. For the individual redshifts, a reexpansion in terms of the symmetric mass ratio $\ensuremath{\nu}$ does not improve the convergence of the series. However we find that when looking at the sum of the redshift factors of both back holes, ${z}_{A}+{z}_{B}$, which is symmetric under the exchange of the masses, a reexpansion in $\ensuremath{\nu}$ accelerates its convergence. Our work provides further evidence of the surprising effectiveness of SMR approximations in modeling even comparable mass binary black holes.

The fifth-order post-Newtonian Hamiltonian dynamics of two-body systems from an effective field theory approach

Within an effective field theory method to general relativity, we calculate the fifth-order post–Newtonian (5PN) Hamiltonian dynamics also for the tail terms, extending earlier work on the potential contributions, working in harmonic coordinates. Here we calculate independently all (local) 5PN far-zone contributions using the in–in formalism, on which we give a detailed account. The five expansion terms of the Hamiltonian in the effective one body (EOB) approach, q82,q63,q44,d5¯ and an, can all be determined from the local contributions to the periastron advance Kloc,h(Eˆ,j), without further assumptions on the structure of the symmetric mass ratio, ν, of the expansion coefficients of the scattering angle χk. The O(ν2) contributions to the 5PN EOB parameters have been unknown in part before. We perform comparisons of our analytic results with the literature and also present numerical results on some observables.

Systematic bias due to eccentricity in parameter estimation for merging binary neutron stars

We study the impact of eccentricity on gravitational-wave parameter estimation for binary neutron star systems. For signals with small eccentricity injected into the advanced LIGO sensitivity, we perform Bayesian parameter estimation using the circular waveform model and show how the recovered parameters can be biased from their true values, focusing on the intrinsic parameters the chirp mass ($M_c$), the symmetric mass ratio ($\eta$), and the tidal deformability ($\tilde{\lambda}$). By comparing the results between the Bayesian and the analytic Fisher-Cutler-Vallisneri (FCV) methods, we obtain the valid criteria for the FCV approach. Employing the FCV method and using the realistic population of binary neutron star sources distributed in the $m_1$-$m_2$-$e_0$ space, where $e_0$ indicates the eccentricity at 10Hz, we calculate the measurement errors ($\sigma_{\theta}$) and the systematic biases ($\Delta \theta/\sigma_{\theta}$) and obtain their generalized distributions in the range of $0 \leq e_0 \leq 0.025$. We find that for all of the three parameters, the biases increase with increasing $e_0$, and this increase is faster for larger $e_0$. The bias is mainly dependent on the value of $e_0$ and weakly dependent on the component masses, and thus the distribution shows a narrow band in the $e_0$-$\Delta \theta/\sigma_{\theta}$ plane. We present various posterior examples to illustrate our new findings, such as the bimodality of posteriors. In particular, we give a specific injection-recovery example to demonstrate the importance of including eccentricity in parameter estimation to avoid incorrect predictions of the neutron star equation of state.

Improvement of the parameter measurement accuracy by the third-generation gravitational wave detector Einstein Telescope

The Einstein Telescope (ET) has been proposed as one of the third-generation gravitational wave (GW) detectors. The sensitivity of ET would be a factor of 10 better than the second-generation GW detector, advanced LIGO (aLIGO); thus, the GW source parameters could be measured with much better accuracy. In this work, we show how the precision in parameter estimation can be improved between aLIGO and ET by comparing the measurement errors. We apply the TaylorF2 waveform model defined in the frequency domain to the Fisher matrix method which is a semi-analytic approach for estimating GW parameter measurement errors. We adopt as our sources low-mass binary black holes with the total masses of M ⩽ 16M ⊙ and the effective spins of −0.9 ⩽ χ eff ⩽ 0.9 and calculate the measurement errors of the mass and the spin parameters using 104 Monte-Carlo samples randomly distributed in our mass and spin parameter space. We find that for the same sources ET can achieve times better signal-to-noise ratio than aLIGO and the error ratios (σ λ,ET/σ λ,aLIGO) for the chirp-mass, symmetric mass ratio, and effective spin parameters can be lower than 7% for all binaries. We also consider the equal-mass binary neutron stars with the component masses of 1, 1.4, and 2M ⊙ and find that the error ratios for the mass and the spin parameters can be lower than 1.5%. In particular, the measurement error of the tidal deformability can also be significantly reduced by ET, with the error ratio of 3.6%–6.1%. We investigate the effect of prior information by applying the Gaussian prior on the coalescence phase ϕ c to the Fisher matrix and find that the error of the intrinsic parameters can be reduced to of the original priorless error if the standard deviation of the prior is similar to .

Generalized quasi-Keplerian solution for eccentric, nonspinning compact binaries at 4PN order and the associated inspiral-merger-ringdown waveform

We derive fourth post-Newtonian (4PN) contributions to the Keplerian-type parametric solution associated with the conservative dynamics of eccentric, non-spinning compact binaries. The solution has been computed while ignoring certain zero-average, oscillatory terms arising due to 4PN tail effects. We provide explicit expressions for the parametric solution and various orbital elements in terms of the conserved energy, angular momentum and symmetric mass ratio. Canonical perturbation theory (along with the technique of Pade approximant) is used to incorporate the 4PN nonlocal-in-time tail effects within the action-angles framework. We then employ the resulting solution to obtain an updated inspiral-merger-ringdown (IMR) waveform that models the coalescence of non-spinning, moderately eccentric black hole binaries, influenced by arXiv:1709.02007. Our updated waveform is expected to be valid over similar parameter range as the above reference. We also present a related waveform which makes use of only the post-Newtonian equations and thus is valid only for the inspiral stage. This waveform is expected to work for a much larger range of eccentricity ($e_t \lesssim 0.85$) than our full IMR waveform (which assumes circularization of the binaries close to merger). We finally pursue preliminary data analysis studies to probe the importance of including the 4PN contributions to the binary dynamics while constructing gravitational waveform templates for eccentric mergers.

Fast frequency-domain effective fly-by waveforms

Recently, we developed effective fly-by (EFB) waveforms designed to model the burst of gravitational radiation from highly eccentric binaries. We here present a faster to evaluate frequency domain EFB waveform. The waveform is constructed through the use of asymptotic expansions of hypergeometric functions. Since the waveform is fully analytic, we study the accuracy to which the binary’s parameters can be measured using a Fisher analysis. We find that degeneracies exist among the parameters, such that the waveform is parameterized in terms of the chirp mass and orbital radius of curvature , instead of the total mass, symmetric mass ratio, and semi-latus rectum of the binary. By computing the Fisher matrix for single bursts from two thousand binary systems, we find that most of the systems will have greater than one hundred percent uncertainty in the chirp mass, luminosity distance, and inclination angle, while roughly half will have less than one hundred percent uncertainty in the orbital radius of curvature, orbital eccentricity, and polarization angle. Further, we repeat this analysis after including additional bursts within the inspiral sequence and find that the uncertainties in the waveform’s parameters can improve by orders of magnitude with a sufficient timing model for the bursts.

Eccentric-orbit extreme-mass-ratio-inspiral radiation. II. 1PN correction to leading-logarithm and subleading-logarithm flux sequences and the entire perturbative 4PN flux

In a recent paper we showed that for eccentric-orbit extreme-mass-ratio inspirals the analytic forms of the leading-logarithm energy and angular momentum post-Newtonian (PN) flux terms (radiated to infinity) can, to arbitrary PN order, be determined by sums over the Fourier spectrum of the Newtonian quadrupole moment. We further showed that an essential part of the eccentricity dependence of the related subleading-logarithm PN sequences, at lowest order in the symmetric mass ratio $\nu$, stems as well from the Newtonian quadrupole moment. Once that part is factored out, the remaining eccentricity dependence is more easily determined by black hole perturbation theory. In this paper we show how the sequences that are the 1PN corrections to the entire leading-logarithm series, namely terms that appear at PN orders $x^{3k+1} \log^k(x)$ and $x^{3k+5/2} \log^k(x)$ (for PN compactness parameter $x$ and integers $k\ge 0$), at lowest order in $\nu$, are determined by the Fourier spectra of the Newtonian mass octupole, Newtonian current quadrupole, and 1PN part of the mass quadrupole moments. We also develop a conjectured (but plausible) form for 1PN correction to the leading logs at second order in $\nu$. Further, in analogy to the first paper, we show that these same source multipole moments also yield nontrivial parts of the 1PN correction to the subleading-logarithm series, and that the remaining eccentricity dependence (at lowest order in $\nu$) can then more easily be determined using black hole perturbation theory. We use this method to determine the entire analytic eccentricity dependence of the perturbative (i.e., lowest order in $\nu$) 4PN non-log terms, $\mathcal{R}_4(e_t)$ and $\mathcal{Z}_4(e_t)$, for energy and angular momentum respectively.

Binary dynamics at the fifth and fifth-and-a-half post-Newtonian orders

Using the new methodology introduced in a recent Letter [Phys.\ Rev.\ Lett.\ {\bf 123}, 231104 (2019)], we present the details of the computation of the conservative dynamics of gravitationally interacting binary systems at the fifth post-Newtonian (5PN) level, together with its extension at the fifth-and-a-half post-Newtonian (5.5PN) level. We present also the sixth post-Newtonian (6PN) contribution to the third-post-Minkowskian (3PM) dynamics. Our strategy combines several theoretical formalisms: post-Newtonian, post-Minkowskian, multipolar-post-Minkowskian, gravitational self-force, effective one-body, and Delaunay averaging. We determine the full functional structure of the 5PN Hamiltonian (which involves 95 non-zero numerical coefficients), except for two undetermined coefficients proportional to the cube of the symmetric mass ratio, and to the fifth and sixth power of the gravitational constant, $G$. We present not only the 5PN-accurate, 3PM contribution to the scattering angle, but also its 6PN-accurate generalization. Both results agree with the corresponding truncations of the recent 3PM result of Bern et al. [Phys.\ Rev.\ Lett.\ {\bf 122}, 201603 (2019)]. We also compute the 5PN-accurate, fourth-post-Minkowskian (4PM) contribution to the scattering angle, including its nonlocal contribution, thereby offering checks for future 4PM calculations. We point out a remarkable hidden simplicity of the gauge-invariant functional relation between the radial action and the effective-one-body energy and angular momentum.

Detection and characterization of spin-orbit resonances in the advanced gravitational wave detectors era

In this paper, we test the performance of templates in detection and characterization of Spin-orbit resonant (SOR) binaries. We use precessing SEOBNRv3 waveforms as well as {\it four} numerical relativity (NR) waveforms to model GWs from SOR binaries and filter them through IMRPhenomD, SEOBNRv4 (non-precessing) and IMRPhenomPv2 (precessing) approximants. We find that IMRPhenomD and SEOBNRv4 recover only $\sim70\%$ of injections with fitting factor (FF) higher than 0.97 (or 90\% of injections with ${\rm FF} >0.9$).However, using the sky-maxed statistic, IMRPhenomPv2 performs magnificently better than their non-precessing counterparts with recovering $99\%$ of the injections with FFs higher than 0.97. Interestingly, injections with $\Delta \phi = 180^{\circ}$ have higher FFs ($\Delta \phi$ is the angle between the components of the black hole spins in the plane orthogonal to the orbital angular momentum) as compared to their $\Delta \phi =0^{\circ}$ and generic counterparts. This implies that we will have a slight observation bias towards $\Delta \phi=180^{\circ}$ SORs while using non-precessing templates for searches. All template approximants are able to recover most of the injected NR waveforms with FFs $>0.95$. For all the injections including NR, the error in estimating chirp mass remains below $<10\%$ with minimum error for $\Delta \phi = 180^{\circ}$ resonant binaries. The symmetric mass ratio can be estimated with errors below $15\%$. The effective spin parameter $\chi_{\rm eff}$ is measured with maximum absolute error of 0.13. The in-plane spin parameter $\chi_p$ is mostly underestimated indicating that a precessing signal will be recovered as a relatively less precessing signal. Based on our findings, we conclude that we not only need improvements in waveform models towards precession and non-quadrupole modes but also better search strategies for precessing GW signals.

Analytic family of post-merger template waveforms

Building on the analytical description of the post-merger (ringdown) waveform of coalescing, non-precessing, spinning, (BBHs) introduced in Phys. Rev. D 90, 024054 (2014), we propose an analytic, closed form, time-domain, representation of the $\ell=m=2$ gravitational radiation mode emitted after merger. This expression is given as a function of the component masses and dimensionless spins $(m_{1,2},\chi_{1,2})$ of the two inspiralling objects, as well as of the mass $M_{\rm BH}$ and (complex) frequency $\sigma_{1}$ of the fundamental quasi-normal mode of the remnant black hole. Our proposed template is obtained by fitting the post-merger waveform part of several publicly available numerical relativity simulations from the Simulating eXtreme Spacetimes (SXS) catalog and then suitably interpolating over (symmetric) mass ratio and spins. We show that this analytic expression accurately reproduces ($\sim$~0.01 rad) the phasing of the post-merger data of other datasets not used in its construction. This is notably the case of the spin-aligned run SXS:BBH:0305, whose intrinsic parameters are consistent with the 90\% credible intervals reported by the parameter-estimation followup of GW150914 in Phys. Rev. Lett. 116 (2016) no.24, 241102. Using SXS waveforms as "experimental" data, we further show that our template could be used on the actual GW150914 data to perform a new measure the complex frequency of the fundamental quasi-normal mode so to exploit the complete (high signal-to-noise-ratio) post-merger waveform.

Deriving analytic solutions for compact binary inspirals without recourse to adiabatic approximations

We utilize the dynamical renormalization group formalism to calculate the real space trajectory of a compact binary inspiral for long times via a systematic resummation of secularly growing terms. This method generates closed form solutions without orbit averaging, and the accuracy can be systematically improved. The expansion parameter is $v^5 \nu \Omega(t-t_0)$ where $t_0$ is the initial time, $t$ is the time elapsed, and $\Omega$ and $v$ are the angular orbital frequency and initial speed, respectively, and $\nu$ is the binary's symmetric mass ratio. We demonstrate how to apply the renormalization group method to resum solutions beyond leading order in two ways. First, we calculate the second order corrections of the leading radiation reaction force, which involves highly non-trivial checks of the formalism (i.e. its renormalizability). Second, we show how to systematically include post-Newtonian corrections to the radiation reaction force. By avoiding orbit averaging we gain predictive power and eliminate ambiguities in the initial conditions. Finally, we discuss how this methodology can be used to find analytic solutions to the spin equations of motion that are valid over long times.

Measuring violations of general relativity from single gravitational wave detection by nonspinning binary systems: Higher-order asymptotic analysis

A frequentist asymptotic expansion method for error estimation is employed for a network of gravitational wave detectors to assess the amount of information that can be extracted from gravitational wave observations. Mathematically we derive lower bounds in the errors that any parameter estimator will have in the absence of prior knowledge to distinguish between the post-Einsteinian (ppE) description of coalescing binary systems and that of general relativity. When such errors are smaller than the parameter value, there is possibility to detect these violations from GR. A parameter space with inclusion of dominant dephasing ppE parameters $(\beta, b)$ is used for a study of first- and second-order (co)variance expansions, focusing on the inspiral stage of a nonspinning binary system of zero eccentricity detectible through Adv. LIGO and Adv. Virgo. Our procedure is an improvement of the Cram\'{e}r-Rao Lower Bound. When Bayesian errors are lower than our bound it means that they depend critically on the priors. The analysis indicates the possibility of constraining deviations from GR in inspiral SNR ($\rho \sim 15-17$) regimes that are achievable in upcoming scientific runs (GW150914 had an inspiral SNR $\sim 12$). The errors on $\beta$ also increase errors of other parameters such as the chirp mass $\mathcal{M}$ and symmetric mass ratio $\eta$. Application is done to existing alternative theories of gravity, which include modified dispersion relation of the waveform, non-spinning models of quadratic modified gravity, and dipole gravitational radiation (i.e., Brans-Dicke type) modifications.

Synergy between ground- and space-based gravitational-wave detectors for estimation of binary coalescence parameters

We study the advantage of the co-existence of future ground and space based gravitational wave detectors, in estimating the parameters of a binary coalescence. Using the post-Newtonian waveform for the inspiral of non-spinning neutron star-black hole pairs in circular orbits, we study how the estimates for chirp mass, symmetric mass ratio, and time and phase at coalescence are improved by combining the data from different space-ground detector pairs. Since the gravitational waves produced by binary coalescence also provide a suitable domain where we can study strong field gravity, we also study the deviations from general relativity using the parameterized post-Einsteinian framework. As an example, focusing on the Einstein telescope and DECIGO pair, we demonstrate that there exists a sweet spot range of sensitivity in the pre-DECIGO phase where the best enhancement due to the synergy effect can be obtained for the estimates of the post-Newtonian waveform parameters as well as the modification parameters to general relativity.

Frequency domain reduced order model of aligned-spin effective-one-body waveforms with generic mass ratios and spins

I provide a frequency domain reduced order model (ROM) for the aligned-spin effective-one-body (EOB) model "SEOBNRv2" for data analysis with second and third generation ground based gravitational wave (GW) detectors. SEOBNRv2 models the dominant mode of the GWs emitted by the coalescence of black hole (BH) binaries. The large physical parameter space (dimensionless spins $-1 \leq \chi_i \leq 0.99$ and symmetric mass-ratios $0.01 \leq \eta \leq 0.25$) requires sophisticated reduced order modeling techniques, including patching in the parameter space and in frequency. I find that the time window over which the inspiral-plunge and the merger-ringdown waveform in SEOBNRv2 are connected is discontinuous when the spin of the deformed Kerr BH $\chi=0.8$ or the symmetric mass-ratio $\eta \sim 0.083$. This discontinuity increases resolution requirements for the ROM. The ROM can be used for compact binary systems with total masses of $2 M_\odot$ or higher for the advanced LIGO (aLIGO) design sensitivity and a $10$ Hz lower cutoff frequency. The ROM has a worst mismatch against SEOBNRv2 of $\sim 1\%$, but in general mismatches are better than $\sim 0.1\%$. The ROM is crucial for key data analysis applications for compact binaries, such as GW searches and parameter estimation carried out within the LIGO Scientific Collaboration (LSC).