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The Advanced LIGO and Virgo gravitational wave observatories have opened a new window with which to study the inspiral and mergers of binary compact objects. These observations are most powerful when coordinated with multi-messenger observations. This was underlined by the first observation of a binary neutron star merger GW170817, coincident with a short Gamma-ray burst, GRB170817A, and the identification of the host galaxy NGC~4993 from the optical counterpart AT~2017gfo. Finding the fast-fading optical counterpart critically depends on the rapid production of a sky-map based on LIGO/Virgo data. Currently, a rapid initial sky map is produced followed by a more accurate, high-latency, $gtrsimSI{12}{hr}$ sky map. We study optimization choices of the Bayesian prior and signal model which can be used alongside other approaches such as reduced order quadrature. We find these yield up to a $60%$ reduction in the time required to produce the high-latency localisation for binary neutron star mergers.
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We discuss gravitational waves from merging binaries using a Newtonian approach with some inputs from the Post-Newtonian formalism. We show that it is possible to understand the key features of the signal using fundamental physics and also demonstrate that an approximate calculation gives us the correct order of magnitude estimate of the parameters describing the merging binary system. We build on this analysis to understand the range for different types of sources for given detector sensitivity. We also consider known binary pulsar systems and discuss the expected gravitational wave signal from these.
The detection of intermediate-mass black holes (IMBHs) i.e. those with mass $sim 100$-$10^5 M_odot$, is an emerging goal of gravitational-wave (GW) astronomy with wide implications for cosmology and tests of strong-field gravity. Current PyCBC-based searches for compact binary mergers, which matched filter the detector data against a set of template waveforms, have so far detected or confirmed several GW events. However, the sensitivity of these searches to signals arising from mergers of IMBH binaries is not optimal. Here, we present a new optimised PyCBC-based search for such signals. Our search benefits from using a targeted template bank, stricter signal-noise discriminators and a lower matched-filter frequency cut-off. In particular, for a population of simulated signals with isotropically distributed spins, we improve the sensitive volume-time product over previous PyCBC-based searches, at an inverse false alarm rate of 100 years, by a factor of 1.5 to 3 depending on the total binary mass. We deploy this new search on Advanced LIGO-Virgo data from the first half of the third observing run. The search does not identify any new significant IMBH binaries but does confirm the detection of the short-duration GW signal GW190521 with a false alarm rate of 1 in 727 years.
To date, close to fifty presumed black hole binary mergers were observed by the LIGO and Virgo detectors. The analyses have been done with an assumption that these objects are black holes by limiting the spin prior to the Kerr bound. However, the above assumption is not valid for superspinars, which have the Kerr geometry but rotate beyond the Kerr bound. In this study, we investigate whether and how the limited spin prior range causes a bias in parameter estimation for superspinars if they are detected. To this end, we estimate binary parameters of the simulated inspiral signals of the gravitational waves of compact binaries by assuming that at least one component of them is a superspinar. We have found that when the primary is a superspinar, both mass and spin parameters are biased in parameter estimation due to the limited spin prior range. In this case, the extended prior range is strongly favored compared to the limited one. On the other hand, when the primary is a black hole, we do not see much bias in parameter estimation due to the limited spin prior range, even though the secondary is a superspinar. We also apply the analysis to black hole binary merger events GW170608 and GW190814, which have a long and loud inspiral signal. We do not see any preference of superspinars from the model selection for both events. We conclude that the extension of the spin prior range is necessary for accurate parameter estimation if highly spinning primary objects are found, while it is difficult to identify superspinars if they are only the secondary objects. Nevertheless, the bias in parameter estimation of spin for the limited spin prior range can be a clue of the existence of superspinars.
Inferring astrophysical information from gravitational waves emitted by compact binaries is one of the key science goals of gravitational-wave astronomy. In order to reach the full scientific potential of gravitational-wave experiments we require techniques to mitigate the cost of Bayesian inference, especially as gravitational-wave signal models and analyses become increasingly sophisticated and detailed. Reduced order models (ROMs) of gravitational waveforms can significantly reduce the computational cost of inference by removing redundant computations. In this paper we construct the first reduced order models of gravitational-wave signals that include the effects of spin-precession, inspiral, merger, and ringdown in compact object binaries, and which are valid for component masses describing binary neutron star, binary black hole and mixed binary systems. This work utilizes the waveform model known as IMRPhenomPv2. Our ROM enables the use of a fast reduced order quadrature (ROQ) integration rule which allows us to approximate Bayesian probability density functions at a greatly reduced computational cost. We find that the ROQ rule can be used to speed up inference by factors as high as 300 without introducing systematic bias. This corresponds to a reduction in computational time from around half a year to a half a day, for the longest duration/lowest mass signals. The ROM and ROQ rule are available with the main inference library of the LIGO Scientific Collaboration, LALInference.
Gravitational waves (GWs) from merging black holes allow for unprecedented probes of strong-field gravity. Testing gravity in this regime requires accurate predictions of gravitational waveform templates in viable extensions of General Relativity. We concentrate on scalar Gauss-Bonnet gravity, one of the most compelling classes of theories appearing as low-energy limit of quantum gravity paradigms, which introduces quadratic curvature corrections to gravity coupled to a scalar field and allows for black hole solutions with scalar-charge. Focusing on inspiralling black hole binaries, we compute the leading-order corrections due to curvature nonlinearities in the GW and scalar waveforms, showing that the new contributions, beyond merely the effect of scalar field, appear at first post-Newtonian order in GWs. We provide ready-to-implement GW polarizations and phasing. Computing the GW phasing in the Fourier domain, we perform a parameter-space study to quantify the detectability of deviations from General Relativity. Our results lay important foundations for future precision tests of gravity with both parametrized and theory-specific searches.
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