Second-generation Gravitational-wave Detectors Research Articles

High-energy Neutrino Emission Associated with Gravitational-wave Signals: Effects of Cocoon Photons and Constraints on Late-time Emission

We investigate prospects for the detection of high-energy neutrinos produced in the prolonged jets of short gamma-ray bursts (sGRBs). The X-ray light curves of sGRBs show extended emission components lasting for 100–1000 s, which are considered to be produced by prolonged engine activity. Jets produced by such activity should interact with photons in the cocoon formed by the propagation of the jet inside the ejecta of neutron star mergers. We calculate neutrino emission from jets produced by prolonged engine activity, taking account of the interaction between photons provided from the cocoon and cosmic rays accelerated in the jets. We find that IceCube-Gen2, a future neutrino telescope, with second-generation gravitational-wave detectors will probably be able to observe neutrino signals associated with gravitational waves with around 10 years of operation, regardless of the assumed value of the Lorentz factor of the jets. Neutrino observations may enable us to constrain the dissipation region of the jets. We apply this model to GRB 211211A, a peculiar long GRB whose origin may be a binary neutron star merger. Our model predicts that IceCube is unlikely to detect any associated neutrinos, but a few similar events will be able to put a meaningful constraint on the physical quantities of the prolonged engine activities.

Einstein Telescope, the future generation of ground based gravitational wave detectors

The second-generation gravitational wave detectors Advanced LIGO and Advanced Virgo have shown their breakthrough capability to shed light on our understanding of the Universe. Although the steady increase in sensitivity, these detectors will hit in the future limitations due to their hosting infrastructures. This is the reason why a new generation of gravitational wave detectors are under studies. The Einstein Telescope (ET) is a planned European 3 rd generation gravitational Wave (GW) Observatory, a new research infrastructure designed to host a detector capable to observe the entire Universe using gravitational waves. ET will be a multi-interferometer observatory aiming to increase a factor ten the sensitivity of previous generation detectors. We will give an overview of the project, describe the main scientific goals and the technological challenges that must be overcome to reach the expected sensitivity.

Gravitational Waves from a Core-Collapse Supernova: Perspectives with Detectors in the Late 2020s and Early 2030s

We studied the detectability and reconstruction of gravitational waves from core-collapse supernova multidimensional models using simulated data from detectors predicted to operate in the late 2020s and early 2030s. We found that the detection range will improve by a factor of around two with respect to the second-generation gravitational-wave detectors, and the sky localization will significantly improve. We analyzed the reconstruction accuracy for the lower frequency and higher frequency portion of supernova signals with a 250 Hz cutoff. Since the waveform’s peak frequencies are usually at high frequencies, the gravitational-wave signals in this frequency band were reconstructed more accurately.

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 .

Characterization of Core Optics in Gravitational-Wave Detectors: Case Study of KAGRA Sapphire Mirrors

We report the characterization of superlow-loss optics used in the second-generation gravitational-wave detectors currently in operation. The sapphire test-mass mirrors in the KAGRA detector are introduced as an example, but the techniques here are common to all detectors. In this work, we discuss mainly the surface topography obtained by interferometric techniques and the optical properties obtained with special setups.

Model-independent measurement of the absolute magnitude of Type Ia supernovae with gravitational-wave sources

The similarity of the absolute luminosity profiles of Type Ia supernovae (SNIe), as one kind of distance indicator, has led their use in extragalactic astronomy as secondary standard candles. In general, the empirical relationship of SNIa on the absolute peak magnitude MB is calibrated by Cepheid variables in the near distance scale and directly extrapolated to much farther distances. Therefore, two main problems arise. First of all, their calibration, in particular the determination of MB, depends on the empirical relationship of Cepheid variables, which suffers from various uncertainties. The second is related to the homogeneity of SNIa in their true MB, which is known to be poor in different environments. The observed gravitational-wave (GW) signal of the coalescence of compact binary systems and their electromagnetic counterparts provide the novel and model-independent way to address these two problems. In the era of second-generation GW detectors, the low-redshift GW sources provide a novel method to calibrate the empirical relationship of SNIa, using their self-calibrated distances. In this paper, we use the event GW170817 to calibrate the empirical relationship in different low redshift ranges, and find that the calibration results are consistent with the ones derived from the Cepheid variables. Moreover, the uncertainties of MB in both methods are also comparable. By the observations of third-generation GW detectors, GW sources can also be used to measure the values of MB for the high-redshift SNIe, which provides a unique opportunity to study the dependence of MB on the local environment, strength of gravity, and the intrinsic properties of the explosion, in addition to test the homogeneity of standard candles. We find that the uncertainties of MB in both high and low redshifts are more than one order of magnitude smaller than the current accuracy.

Empirical tests of the black hole no-hair conjecture using gravitational-wave observations

We show that second-generation gravitational-wave detectors at their design sensitivity will allow us to directly probe the ringdown phase of binary black hole coalescences. This opens the possibility to test the so-called black hole no-hair conjecture in a statistically rigorous way. Using state-of-the-art numerical relativity-tuned waveform models and dedicated methods to effectively isolate the quasi-stationary perturbative regime where a ringdown description is valid, we demonstrate the capability of measuring the physical parameters of the remnant black hole, and subsequently determining parameterized deviations from the ringdown of Kerr black holes. By combining information from $\mathcal{O}(5)$ binary black hole mergers with realistic signal-to-noise ratios achievable with the current generation of detectors, the validity of the no-hair conjecture can be verified with an accuracy of $\sim 1.5\%$ at $90\%$ confidence.

Construction of KAGRA: an underground gravitational-wave observatory

Major construction and initial-phase operation of a second-generation gravitational-wave detector KAGRA has been completed. The entire 3-km detector is installed underground in a mine in order to be isolated from background seismic vibrations on the surface. This allows us to achieve a good sensitivity at low frequencies and high stability of the detector. Bare-bones equipment for the interferometer operation has been installed and the first test run was accomplished in March and April of 2016 with a rather simple configuration. The initial configuration of KAGRA is named {\it iKAGRA}. In this paper, we summarize the construction of KAGRA, including the study of the advantages and challenges of building an underground detector and the operation of the iKAGRA interferometer together with the geophysics interferometer that has been constructed in the same tunnel.

Parameter estimation for heavy binary-black holes with networks of second-generation gravitational-wave detectors

The era of gravitational-wave astronomy has started with the discovery of the binary black hole coalescences (BBH) GW150914 and GW151226 by the LIGO instruments. These systems allowed for the first direct measurement of masses and spins of black holes. The component masses in each of the systems have been estimated with uncertainties of over 10\%, with only weak constraints on the spin magnitude and orientation. In this paper we show how these uncertainties will be typical for this type of source when using advanced detectors. Focusing in particular on heavy BBH of masses similar to GW150914, we find that typical uncertainties in the estimation of the source-frame component masses will be around 40\%. We also find that for most events the magnitude of the component spins will be estimated poorly: for only 10\% of the systems the uncertainties in the spin magnitude of the primary (secondary) BH will be below 0.7 (0.8). Conversely, the effective spin along the angular momentum can be estimated more precisely than either spins, with uncertainties below 0.16 for 10\% of the systems. We also quantify how often large or negligible primary spins can be excluded, and how often the sign of the effective spin can be measured. We show how the angle between the spin and the orbital angular momentum can only seldom be measured with uncertainties below 60$^\circ$. We then investigate how the measurement of spin parameters depends on the inclination angle and the total mass of the source. We find that when precession is present, uncertainties are smaller for systems observed close to edge-on. Contrarily to what happens for low-mass, inspiral dominated, sources, for heavy BBH we find that large spins aligned with the orbital angular momentum can be measured with small uncertainty. We also show how spin uncertainties increase with the total mass. Finally...

The Advanced LIGO photon calibrators.

The two interferometers of the Laser Interferometry Gravitational-wave Observatory (LIGO) recently detected gravitational waves from the mergers of binary black hole systems. Accurate calibration of the output of these detectors was crucial for the observation of these events and the extraction of parameters of the sources. The principal tools used to calibrate the responses of the second-generation (Advanced) LIGO detectors to gravitational waves are systems based on radiation pressure and referred to as photon calibrators. These systems, which were completely redesigned for Advanced LIGO, include several significant upgrades that enable them to meet the calibration requirements of second-generation gravitational wave detectors in the new era of gravitational-wave astronomy. We report on the design, implementation, and operation of these Advanced LIGO photon calibrators that are currently providing fiducial displacements on the order of 10-18m/Hz with accuracy and precision of better than 1%.

Detecting black-hole binary clustering via the second-generation gravitational-wave detectors

The first discovery of the gravitational wave (GW) event, GW150914, suggests a higher merger rate of black-hole (BH) binaries. If this is true, a number of BH binaries will be observed via the second-generation GW detectors, and the statistical properties of the observed BH binaries can be scrutinized. A naive but important question to ask is whether the spatial distribution of BH binaries faithfully traces the matter inhomogeneities in the Universe or not. Although the BH binaries are thought to be formed inside the galaxies in most of the scenarios, there is no observational evidence to confirm such a hypothesis. Here, we estimate how well the second-generation GW detectors can statistically confirm the BH binaries to be a tracer of the large-scale structure by looking at the auto- and cross-correlation of BH binaries with photometric galaxies and weak lensing measurements, finding that, with a 3 year observation, the $>3\sigma$ detection of non-zero signal is possible if the BH merger rate today is $\dot{n}_0\gtrsim100$ Gpc$^{-3}$yr$^{-1}$ and the clustering bias of BH binaries is $b_{\rm BH,0}\gtrsim1.5$.

Observation of reduction of radiation-pressure-induced rotational anti-spring effect on a 23 mg mirror in a Fabry–Perot cavity

Although quantum radiation pressure noise could limit the sensitivity of the second-generation gravitational wave detectors, it has not been observed in a broad frequency band and its reduction methods have not been proven yet. A promising way to observe quantum radiation pressure noise is to store high power light in an optical cavity with a tiny mirror. However, anti-spring torque caused by radiation pressure of the light acting on the tiny mirror could make the system unstable, and it is generally difficult to attach actuators to the tiny mirror for stabilization. Hence a new method to overcome this anti-spring torque has been developed. In the new method, the other mirror of the cavity is controlled so that the position of the resonant light at the tiny mirror is fixed to decrease the anti-spring torque and stabilize angular motion of the tiny mirror. With the new method, it was successfully observed that the anti-spring torque caused by radiation pressure was suppressed in the present experiment with a 23 mg mirror, where resonant frequency of angular motion of the tiny mirror increased towards the mechanical resonant frequency.

Measurement of Schumann Resonance at Kamioka

On the stochastic gravitational-wave search, correlated noise in two or more gravitational-wave detectors can be a serious problem. Schumann resonance is the name of a standing wave of electromagnetic fields, which is one of the correlated noise sources for the second-generation gravitational-wave detectors. We measured the noise levels of the environmental magnetic field both inside and outside the mine of KAGRA site at Kamioka. In this letter, we report the result of the measurement and compare the amplitude of magnetic fields inside and outside the mine to find possible issues or gain of constructing a detector underground.

Detecting quasinormal modes of binary black hole mergers with second-generation gravitational-wave detectors

Recent population synthesis simulations of Pop III stars suggest that the event rate of coalescence of $\sim 30M_\odot$--$30M_\odot$ binary black holes can be high enough for the detection by the second generation gravitational wave detectors. The frequencies of chirp signal as well as quasinormal modes are near the best sensitivity of these detectors so that it would be possible to confirm Einstein's general relativity. Using the WKB method, we suggest that for the typical value of spin parameter $a/M\sim 0.7$ from numerical relativity results of the coalescence of binary black holes, the strong gravity of the black hole space-time at around the radius $2M$, which is just $\sim 1.17$ times the event horizon radius, would be confirmed as predicted by general relativity. The expected event rate with the signal-to-noise ratio $> 35$ needed for the determination of the quasinormal mode frequency with the meaningful accuracy is $0.17$--$7.2$~${\rm events~yr^{-1}~(SFR_p/(10^{-2.5}~M_\odot~yr^{-1}~Mpc^{-3}))} \cdot (\rm [f_b/(1+f_b)]/0.33)$ where ${\rm SFR_p}$ and ${\rm f_b}$ are the peak value of the Pop III star formation rate and the fraction of binaries, respectively. As for the possible optical counter part, if the merged black hole of mass $M\sim 60M_\odot$ is in the interstellar matter with $n\sim 100~{\rm cm^{-3}}$ and the proper motion of black hole is $\sim 1~{\rm km~s^{-1}}$, the luminosity is $\sim 10^{40}~{\rm erg~ s^{-1}}$ which can be detected up to $\sim 300~{\rm Mpc}$, for example, by Subaru-HSC and LSST with the limiting magnitude 26.

Detecting Gravitational-Wave Transients at 5σ: A Hierarchical Approach.

As second-generation gravitational-wave detectors prepare to analyze data at unprecedented sensitivity, there is great interest in searches for unmodeled transients, commonly called bursts. Significant effort has yielded a variety of techniques to identify and characterize such transient signals, and many of these methods have been applied to produce astrophysical results using data from first-generation detectors. However, the computational cost of background estimation remains a challenging problem; it is difficult to claim a 5σ detection with reasonable computational resources without paying for efficiency with reduced sensitivity. We demonstrate a hierarchical approach to gravitational-wave transient detection, focusing on long-lived signals, which can be used to detect transients with significance in excess of 5σ using modest computational resources. In particular, we show how previously developed seedless clustering techniques can be applied to large data sets to identify high-significance candidates without having to trade sensitivity for speed.

Measuring Intermediate-Mass Black-Hole Binaries with Advanced Gravitational Wave Detectors.

We perform a systematic study to explore the accuracy with which the parameters of intermediate-mass black-hole binary systems can be measured from their gravitational wave (GW) signatures using second-generation GW detectors. We make use of the most recent reduced-order models containing inspiral, merger, and ringdown signals of aligned-spin effective-one-body waveforms to significantly speed up the calculations. We explore the phenomenology of the measurement accuracies for binaries with total masses between 50M(⊙) and 500M(⊙) and mass ratios between 0.1 and 1. We find that (i) at total masses below ∼200M(⊙), where the signal-to-noise ratio is dominated by the inspiral portion of the signal, the chirp mass parameter can be accurately measured; (ii) at higher masses, the information content is dominated by the ringdown, and total mass is measured more accurately; (iii) the mass of the lower-mass companion is poorly estimated, especially at high total mass and more extreme mass ratios; and (iv) spin cannot be accurately measured for our injection set with nonspinning components. Most importantly, we find that for binaries with nonspinning components at all values of the mass ratio in the considered range and at a network signal-to-noise ratio of 15, analyzed with spin-aligned templates, the presence of an intermediate-mass black hole with mass >100M(⊙) can be confirmed with 95% confidence in any binary that includes a component with a mass of 130M(⊙) or greater.

DOUBLE COMPACT OBJECTS. III. GRAVITATIONAL-WAVE DETECTION RATES

The unprecedented range of second-generation gravitational-wave (GW) observatories calls for refining the predictions of potential sources and detection rates. The coalescence of double compact objects (DCOs)---i.e., neutron star-neutron star (NS-NS), black hole-neutron star (BH-NS), and black hole-black hole (BH-BH) binary systems---is the most promising source of GWs for these detectors. We compute detection rates of coalescing DCOs in second-generation GW detectors using the latest models for their cosmological evolution, and implementing inspiral-merger-ringdown (IMR) gravitational waveform models in our signal-to-noise ratio calculations. We find that: (1) the inclusion of the merger/ringdown portion of the signal does not significantly affect rates for NS-NS and BH-NS systems, but it boosts rates by a factor $\sim 1.5$ for BH-BH systems; (2) in almost all of our models BH-BH systems yield by far the largest rates, followed by NS-NS and BH-NS systems, respectively, and (3) a majority of the detectable BH-BH systems were formed in the early Universe in low-metallicity environments. We make predictions for the distributions of detected binaries and discuss what the first GW detections will teach us about the astrophysics underlying binary formation and evolution.

Design study of the KAGRA output mode cleaner

Most second-generation gravitational-wave detectors employ an optical resonator called an output mode cleaner (OMC), which filters out junk light from the signal and the reference light, before it reaches the detection photodiode located at the asymmetric port of the large-scale interferometer. The optical parameters of the OMC should be carefully chosen to satisfy the requirements to filter out unwanted light whilst transmitting the gravitational-wave signal. We use the simulation program FINESSE and realistic mirror phase maps that have the same surface quality as the KAGRA test masses to find out a proper design of the KAGRA OMC.

Pre-merger localization of eccentric compact binary coalescences with second-generation gravitational-wave detector networks

We study the possibility of pre-merger localization of eccentric compact binary coalescences by second-generation gravitational-wave detector networks. Gravitational waves from eccentric binaries can be regarded as a sequence of pulses, which are composed of various higher harmonic modes than ones with twice the orbital frequency. The higher harmonic modes from a very early inspiral phase will not only contribute to the signal-to-noise ratio, but also allow us to localize the gravitational-wave source before the merger sets in. This is due to the fact that high-frequency gravitational waves are essential for the source localization via triangulation by ground-based detector networks. We found that the single-detector signal-to-noise ratio exceeds 5 at 10 min before the merger for a 1.4--1.4 $M_\odot$ eccentric binary neutron stars at 100 Mpc in optimal cases, and it can be localized up to 10 deg$^2$ at half a minute before the merger by a four-detector network. We will even be able to achieve $\sim$ 10 deg$^2$ at 10 min before the merger for a face-on eccentric compact binary by a five-detector network.

Method to reduce excess noise of a detuned cavity for application in KAGRA

Ground-based gravitational-wave detectors are based on high precision laser interferometry. One promising technique to improve the detector’s sensitivity is the detuning of an optical cavity, which enhances the signal at around certain frequencies for target astronomical sources. The detuning, however, involves technical noise due to an asymmetry of the control sidebands, which includes photo-detector noise and oscillator-phase noise. Here, we introduce a solution to reduce the two kinds of excess noise using an amplitude-modulation sideband that compensates the asymmetry. The solution is planned to be implemented in the Japanese second-generation gravitational-wave detector KAGRA.