In an earlier work [S. Kastha et al., PRD {bf 98}, 124033 (2018)], we developed the {it parametrized multipolar gravitational wave phasing formula} to test general relativity, for the non-spinning compact binaries in quasi-circular orbit. In this pap
er, we extend the method and include the important effect of spins in the inspiral dynamics. Furthermore, we consider parametric scaling of PN coefficients of the conserved energy for the compact binary, resulting in the parametrized phasing formula for non-precessing spinning compact binaries in quasi-circular orbit. We also compute the projected accuracies with which the second and third generation ground-based gravitational wave detector networks as well as the planned space-based detector LISA will be able to measure the multipole deformation parameters and the binding energy parameters. Based on different source configurations, we find that a network of third-generation detectors would have comparable ability to that of LISA in constraining the conservative and dissipative dynamics of the compact binary systems. This parametrized multipolar waveform would be extremely useful not only in deriving the first upper limits on any deviations of the multipole and the binding energy coefficients from general relativity using the gravitational wave detections, but also for science case studies of next generation gravitational wave detectors.
In a recent letter [N. V. Krishnendu et al., PRL 119, 091101 (2017)] we explored the possibility of probing the binary black hole nature of coalescing compact binaries, by measuring their spin-induced multipole moments, observed in advanced LIGO dete
ctors. Coefficients characterizing the spin-induced multipole moments of Kerr black holes are predicted by the no-hair conjecture and appear in the gravitational waveforms through quadratic and higher order spin interactions and hence can be directly measured from gravitational wave observations. We assess the capabilities of the third-generation gravitational wave interferometers such as Cosmic Explorer and Einstein Telescope in carrying out such measurements and use them to test the binary black hole nature of observed binaries. In this paper, we extend the investigations of our previous work, by proposing to measure (a) spin-induced quadrupole effects, (b) simultaneous measurements of spin-induced quadrupole and octupole effects, in the context of the third-generation detectors. We find that, using third-generation detectors the symmetric combination of coefficients associated with spin-induced quadrupole moment of each binary component may be constrained to a value $leq 1.1$ while a similar combination of coefficients for spin-induced octupole moment may be constrained to $leq 2$, where both combinations take the value of 1 for a binary black hole system. Further, we consider two different binary black hole populations, as proxies of the population that will be observed by the third generation detectors, and obtain the resulting distribution of the spin-induced quadrupole coefficient. These estimates suggest that third-generation detectors can accurately constrain the first four multipole moments of the compact objects (mass, spin, quadrupole, and octupole) facilitating a thorough probe of their black hole nature.
We propose a novel method to test the consistency of the multipole moments of compact binary systems with the predictions of General Relativity (GR). The multipole moments of a compact binary system, known in terms of symmetric and trace-free tensors
, are used to calculate the gravitational waveforms from compact binaries within the post-Newtonian (PN) formalism. For nonspinning compact binaries, we derive the gravitational wave phasing formula, in the frequency domain, parametrizing each PN order term in terms of the multipole moments which contribute to that order. Using GW observations, this {it{parametrized multipolar phasing}} would allow us to derive the bounds on possible departures from the multipole structure of GR and hence constrain the parameter space of alternative theories of gravity. We compute the projected accuracies with which the second generation ground-based detectors, such as Advanced Laser Interferometer Gravitational-wave Observatory (LIGO), the third generation detectors such as Einstein Telescope and Cosmic Explorer, as well as space-based detector Laser Interferometer Space Antenna (LISA) will be able to measure these multipole parameters. We find that while Advanced LIGO can measure the first two or three multipole coefficients with good accuracy, Cosmic Explorer and Einstein Telescope may be able to measure the first four multipole coefficients which enter the phasing formula. Intermediate mass ratio inspirals, with mass ratio of several tens, in the frequency band of planned space-based LISA mission should be able to measure all the seven multipole coefficients which appear in the 3.5PN phasing formula. Our finding highlights the importance of this class of sources for probing the strong-field gravity regime. The proposed test will facilitate the first probe of the multipolar structure of Einsteins general relativity.
We propose a novel method to test the binary black hole (BBH) nature of compact binaries detectable by gravitational wave (GW) interferometers and hence constrain the parameter space of other exotic compact objects. The spirit of the test lies in the
no-hair conjecture for black holes where all properties of a black hole are characterised by the mass and the spin of the black hole. The method relies on observationally measuring the quadrupole moments of the compact binary constituents induced due to their spins. If the compact object is a Kerr black hole (BH), its quadrupole moment is expressible solely in terms of its mass and spin. Otherwise, the quadrupole moment can depend on additional parameters (such as equation of state of the object). The higher order spin effects in phase and amplitude of a gravitational waveform, which explicitly contains the spin-induced quadrupole moments of compact objects, hence uniquely encodes the nature of the compact binary. Thus we argue that an independent measurement of the spin-induced quadrupole moment of the compact binaries from GW observations can provide a unique way to distinguish binary BH systems from binaries consisting of exotic compact objects.
With the high sensitivity and wide-field coverage of the Square Kilometre Array (SKA), large samples of explosive transients are expected to be discovered. Radio wavelengths, especially in commensal survey mode, are particularly well suited for uncov
ering the complex transient phenomena. This is because observations at radio wavelengths may suffer less obscuration than in other bands (e.g. optical/IR or X-rays) due to dust absorption. At the same time, multiwaveband information often provides critical source classification rapidly than possible with only radio band data. Therefore, multiwaveband observational efforts with wide fields of view will be the key to progress of transients astronomy from the middle 2020s offering unprecedented deep images and high spatial and spectral resolutions. Radio observations of gamma ray bursts (GRBs) with SKA will uncover not only much fainter bursts and verifying claims of sensitivity limited population versus intrinsically dim GRBs, they will also unravel the enigmatic population of orphan afterglows. The supernova rate problem caused by dust extinction in optical bands is expected to be lifted in the SKA era. In addition, the debate of single degenerate scenario versus double degenerate scenario will be put to rest for the progenitors of thermonuclear supernovae, since highly sensitive measurements will lead to very accurate mass loss estimation in these supernovae. One also expects to detect gravitationally lensed supernovae in far away Universe in the SKA bands. Radio counterparts of the gravitational waves are likely to become a reality once SKA comes online. In addition, SKA is likely to discover various new kinds of transients.
The LISA Parameter Estimation (LISAPE) Taskforce was formed in September 2007 to provide the LISA Project with vetted codes, source distribution models, and results related to parameter estimation. The Taskforces goal is to be able to quickly calcula
te the impact of any mission design changes on LISAs science capabilities, based on reasonable estimates of the distribution of astrophysical sources in the universe. This paper describes our Taskforces work on massive black-hole binaries (MBHBs). Given present uncertainties in the formation history of MBHBs, we adopt four different population models, based on (i) whether the initial black-hole seeds are small or large, and (ii) whether accretion is efficient or inefficient at spinning up the holes. We compare four largely independent codes for calculating LISAs parameter-estimation capabilities. All codes are based on the Fisher-matrix approximation, but in the past they used somewhat different signal models, source parametrizations and noise curves. We show that once these differences are removed, the four codes give results in extremely close agreement with each other. Using a code that includes both spin precession and higher harmonics in the gravitational-wave signal, we carry out Monte Carlo simulations and determine the number of events that can be detected and accurately localized in our four population models.
The paper summarizes the parallel session B3 {em Analytic approximations, perturbation methods, and their applications} of the GR18 conference. The talks in the session reported notably recent advances in black hole perturbations and post-Newtonian a
pproximations as applied to sources of gravitational waves.
