| Title | Author(s) | Abstract |
|---|---|---|
| Status of KAGRA calibration system upgrade toward O4 | Dan Chen(NAOJ), KAGRA Collaboration | Precise calibration of a telescope is important to make scientifically meaningful gravitational wave observations. Photon calibrator (Pcal) is a main calibration tool for KAGRA. We used Pcal to calibrate the observed signal of KAGRA during O3 and successful released reconstructed h(t) in November 2020. We are upgrading the calibration system in order to meet O4 requirements and improve issues we found during O3. Our current main activities are (A) Improvement of absolute calibration error for Pcal (B) Pcal laser noise improvement to meet O4 KAGRA sensitivity requirement (C) Improvement of beam alignment system We will report the current status of the calibration system upgrade including the above items. |
| On Improving Glitch Classification Performance for Gravitational Wave Detection using Generative Adversarial Networks | Jianqi Yan (MUST, Macau), Alex P. Leung (MUST, Macau), C. Y. Hui (Chungnam National University) | Identifying and pinpointing the nature of unwanted non-Gaussian noise anomalies from the gravitational wave detectors (i.e. glitches) are important for preventing false alarms and improving the instrumental performance. In this work, we aim to improve glitch classification with spectrograms. We propose to perform data augmentation with ProGAN which is a variant of Generative Adversarial Networks (GANs) for enlarging the sample size and resolving the issue of data imbalance problem. Using the Gravity Spy dataset in our experiments, we demonstrate that the proposed method with using ProGAN for increasing the number of training spectrograms can improve the generalization performance of glitch classification significantly. The state-of-the-art accuracy of 99.21% is achieved for glitch classification on the Gravity Spy dataset. The spectrograms of the unidentified nature can further be analyzed and classified with our method. |
| Status of KAGRA cryogenics | Takafumi Ushiba on behalf of the KAGRA collaboration | Cooling sapphire mirrors at 20 K for reducing thermal noise is one of the unique key features of KAGRA. However, cooling mirrors have technical difficulties. One large issue for cooling mirrors is a "frost" problem, which have been observed several times during O3 commissioning term. Frost on the mirror reduces finesse of the arm cavities and disturbs an interferometer operation. In addition, frost on the viewports disturbs the local control of the suspensions. Thus, cooling scheme to avoid frosting on the mirrors and viewports are essential technique for cooling the mirrors. From November of 2020 to February of 2021, we performed a cooling test of KAGRA cryogenic payload. During this test, we cooled the cryostat step by step: cooling duct shield first, radiation shields second, and the payload last. At each stage of cooling, we visually inspected the viewport and mirror surfaces and no frost could be observed. So, we plan to cool the mirror according this procedure from next time. In this talk, detail of the experiment and cooling procedure will be discussed. |
| Multi-Messenger Astronomy Efforts in Korea: GW EM Counterpart Korean Observatory (GECKO) | Myungshin Im | In this talk, we will introduce the multi-messenger astronomy (MMA) EM follow-up observation efforts in Korea. To rapidly identify and characterize EM counterparts of GW events, we have organized the GW EM Counterpart Korean Observatory (GECKO). We will describe observational capabilities of GECKO, and the GECKO results from O2/O3 runs. We will also give future prospects of GECKO and other ongoing MMA activities, in particular related to the optical follow-up observations. |
| Rapid Generation of Kilonova Light Curves Using Variational Autoencoder | Surojit Saha,Michael J. Williams, Laurence Datrier, Matt Nichols, Fergus Hayes, IK Siong Heng, Albert Kong, Martin Hendry, Daniel Williams, Nicola De Lillo | The discovery of the optical counterpart, along with the gravitational waves from GW170817, of the first binary neutron star merger, opened up a new era for multi-messenger astrophysics. The optical counterpart, designated as a kilonova (KN), has immense potential to reveal the nature of compact binary merging systems. Ejecta properties from the merging system provide important information about the total binary mass, the mass ratio, system geometry, and the equation of state of the merging system. In this study, a neural network has been applied to learn the optical light curves of the KN associated with GW170817 using real data and we generate the light curves based on different ejecta properties such as lanthanide fraction, ejecta velocity and ejecta mass. For training the autoencoder, we use simulated KN light curves, where each light curve depends on ejecta mass, ejecta velocity and lanthanide fraction of the ejecta. We generated the light curves using our basic autoencoder code, which, as expected, is quite in agreement with the original light curves. Next, in order to verify the model built from the autoencoder, we apply denoising autoencoder to separate the noisy data from the real data. This process establishes the accuracy and robustness of the code. Following this we, develop conditional variational autoencoder (CVAE), which is for generating light curves based on the physical parameter of our choice. This flexibility was absent in the initial stages. Using the conditional variational autoencoder on simulated data and completing the training process, we generate light curves based on physical parameter of our choice. We have verified that, for a physical parameter present in the simulated data, the generated light curve for the same physical parameter is quite accurate with the original input light curve. This confirms that the code can now generate light curves for any random feasible physical parameter with satisfying accuracy. The timeline for generating the light curves using CVAE is very small, due to which this technique has the ability to replace time consuming and resource-draining simulations. Using the CVAE, we can look into the extremum detection limit associated with a KN model. Since there are several other factors that influences the KN, CVAE trained with simulated data from model with more detailed inclusion physical parameters could give a more insight into the physics of KN. |
| Modelling frequency domain inspiral-merger-ringdown waveforms for eccentric binary black hole mergers | Tamal RoyChowdhury (Indian Institute of Technology Madras), Abhishek Chattaraj (Indian Institute of Technology Madras),, Pranav Satheesh (Indian Institute of Technology Madras),, Chandra Kant Mishra (Indian Institute of Technology Madras) | Gravitational waves detected so far by the LIGO and Virgo detectors can safely be assumed to be the coalescences of binary black holes in quasi-circular orbits. However, the data associated with GW190521 observed in the third-observation run hints at it being a potential eccentric merger. As LIGO and Virgo detectors undergo planned upgrades and the ground based network grows with the addition of detectors such as KAGRA and LIGO-India, we hope to be able to detect systems with residual eccentricities which further necessitates the need for eccentric models for data analysis purposes. Construction of inspiral-merger-ringdown waveforms from binary black mergers in eccentric orbits is explored using gravitational wave phenomenology. Time-domain hybrids (target signals) for training and testing of the signal models are constructed using inputs from the post-Newtonian theory and publicly available numerical relativity simulations for non-spinning binary black holes. Additionally, the effect of including the higher order modes of gravitational radiation on the detection and parameter estimation of eccentric mergers is discussed. |
| GECKO Optical Follow-up Observation of Three Binary Black Hole Merger Events | Joonho Kim (SNU), Myungshin Im (SNU), Gregory S. H. Paek (SNU), Chung-Uk Lee (KASI), Seung-Lee Kim (KASI), Seo-Won Chang (SNU), Changsu Choi (SNU), Sungyong Hwang (SNU), Wonseok Kang (DOAO), Sophia Kim (SNU), Taewoo Kim (DOAO), Hyung Mok Lee (SNU), Gu Lim (SNU), Jinguk Seo (SNU), and Hyun-Il Sung (KASI) | We present optical follow-up observation results of three binary black hole merger (BBH) events, GW190408 181802, GW190412, and GW190503 185404, which were detected by the Advanced Ligo and Virgo gravitational wave (GW) detectors. Electromagnetic (EM) counterparts are generally not expected for BBH merger events, however, some theoretical models suggest that EM counterparts of BBH can possibly arise in special environments. To identify EM counterparts of the three BBH merger events, we observed high-credibility regions of the sky with telescopes of the Gravitational-wave EM Counterpart Korean Observatory (GECKO), including the Korea Microlensing Telescope Network (KMTNet). Our observation started as soon as 100 minutes after the GW event alert and covered roughly 29 - 63 deg2 for each event with a depth of 22.5 mag in R-band within hours of observation. No plausible EM counterparts were found for these events. Our result gives a great promise for the GECKO facilities to find EM counterparts within few hours from GW detection in future GW observation runs. |
| Status of the frequency dependent squeezing experiment in TAMA | Koji Arai (LIGO), Naoki Aritomi (NAOJ), Yoichi Aso (NAOJ), Matteo Barsuglia (APC), Eleonora Capocasa (APC), Marc Eisenmann (NAOJ), Raffaele Flaminio (LAPP), Yuefan Guo (NIKHEF), Yao-Chin Huang (National Tsing-Hua University), Ray-Kuang Lee ( National Tsing-Hua University), Matteo Leonardi (NAOJ), Harald Luck (AEI), Osamu Miyakawa (ICRR), Michael Page (NAOJ), ELeonora Polini (LAPP), Pierre Prat (APC), Ayaka Shoda (NAOJ), Matteo Tacca (NIKHEF), Ryutaro Takahashi (NAOJ), Akihiro Tomura (University of Electro-Communications), Henning Vahlbruch (AEI), Marco Vardaro (NIKHEF), Chien-Ming Wu (National Tsing-Hua University), Yuhang Zhao (NAOJ) | With the improvement of their sensitivities, all ground-based interferometric gravitational waves detectors are going to be limited by quantum noise over an important part of the sensitivity spectrum. Because this quantum noise is due vacuum state entering the detector through the detection port, acting of this quantum state allows to reshape the quantum noise. For instance, the use of frequency dependent squeezed vacuum states allow to achieve a broadband reduction of the quantum noise and is therefore planned to be installed of these detectors. Following the first demonstration of the generation of frequency dependent squeezed vacuum states in the TAMA infrastructure, we are now improving the quality of the frequency dependent squeezed vacuum states as well as demonstrating new control scheme. |
| Determination of the Laser Power on the Photosensors for the IMC Instrumented Baffle | As part of the upgrade program of the Advanced Virgo interferometer, the installation of new instrumented baffles surrounding the main test masses is foreseen. As a demonstrator, and to validate the technology, the existing baffle in the area of the input mode cleaner end-mirror has been replaced by a baffle equipped with photodiodes. This paper presents detailed simulations of the light distribution on the input mode cleaner baffle. They served to validate the proposed layout of the sensors in the baffle, and determine the light exposure of the photodiodes under different scenarios of the interferometer operations, in order to define mitigation strategies for preserving the detector integrity. | |
| Effects of lightning strokes on KAGRA observatory | Tatsuki Washimi (NAOJ) | For ground-based gravitational-wave (GW) detectors, lightning strokes in the atmosphere are sources of environmental noise. Some GW detectors are constructed or planned in underground facilities, and knowledge of how lightning strokes affect them is of interest. This talk is based on our paper: First, the lightning detection system in KAGRA is introduced. Second, the properties of the magnetic field measured inside and outside the KAGRA tunnel are shown. Third, one lightning-induced event in the GW channel of the KAGRA main interferometer is also exhibited. |
| Measurement of Internal Stress from KAGRA Sized Sapphire Substrates | Simon Zeidler (Rikkyo University), Matteo Leonardi (NAOJ), Pengbo Li (Wuhang University) | Birefringence in Sapphire is one of the main problems which currently limits the sensitivity of cryogenic gravitational-waves detectors, such as KAGRA in Japan, which use large Sapphire crystals as mirror substrates for their input and end test-masses. In order to solve the issues (e.g., power sloshing) that arise with birefringence, a proper understanding about its occurrence in Sapphire crystals is mandatory. At the National Astronomical Observatory of Japan (NAOJ), we have successfully established a measurement device for the spatial characterization of large Sapphire samples (Ø: ≤ 22cm; d: ≤ 15cm) . We are able to resolve the distribution of birefringence as 2-dimensional maps with resolutions down to 0.3×0.3mm and can use the obtained information to conclude about the internal stress which is likely to be the main cause of the birefringence. Here, we are presenting the latest results of our measurements, using real-sized Sapphire substrates which were deselected from usage in KAGRA due to other reasons and our calculations to for the internal stress deduction. |
| Study on an Efficient Template Placement Algorithm for CBC Searches in GW Data | Takashi Kato (ICRR, U.Tokyo), Hideyuki Tagoshi (ICRR, U.Tokyo) | For searches of gravitational waves from compact binary coalescence, usually Matched Filtering method with template bank is used. Template bank reflects characteristics of detectors and affects the effectualness of search. For faster and more accurate searches, we introduce a new algorithm for template bank construction based on a previous study (J.Roulet et al., 2019). In our work, we consider both the geometry of parameter space and the distribution of template points. Finally, we confirmed that our new template bank is more accurate and computationally fast. This algorithm can also be useful to respond to instrumental updates rapidly. |
| A Distinguish Method of Binary Black Hole and Black Hole Encounter Gravitational Waves Using Machine Learning | Weichangfeng Guo (Beijing Normal University), Ik Siong Heng (University of Glasgow), Daniel Williams (University of Glasgow), Hunter Gabbard (University of Glasgow), Zong-Hong Zhu (Beijing Normal University) | Black hole(BH) encounter has been regarded as an important sources of gravitational waves(GWs), of which the formation processes is a gravitational radiation driven capture. The BH binaries that form this way have significant eccentricities, and lack a long inspiral phase. When a binary black hole(BBH) merger event like GW190521 reaches such a high mass that its inspiral portion is below the frequencies that the detectors are sensitive, it may appear similar to BH encounters in current detectors.Therefore, future GW events may be misclassified. We first inject large-scale encounter waveforms. Then VItamin, a pre-trained neural network on non-spinning BBH signals, is adopted for fast Bayesian parameter estimates (~20 seconds for one signal, while a typical Bayesian inference takes ~5 hours). We adjust the injections so that the posteriors obtained by VItamin appear to be similar to the BBH. Then we perform PE run on the encounters with BBH-like posterior by Bilby, and injected BBH using medians of samples to see how BBH mimic BH encounter. Here we show that with appropriate injections, the BH encounter can be inferred to credible posterior distributions using BBH template. Therefore, this possibility should be considered for future GW events that lack the inspiral portion. Furthermore, we show a machine learning method to quickly confirm the possibility of BH encounter GW event being mistaken for BBH through the distribution of characteristic J-S divergence. |
| Mass-spin Re-Parameterization for Rapid PE of Inspiral Gravitational-Wave Signals | Eunsub Lee (Institute for Cosmic Ray Research), Soichiro Morisaki (University of Wisconsin-Milwaukee), Hideyuki Tagoshi (Institute for Cosmic Ray Research) | The Markov Chain Monte Carlo(MCMC) is one of the most practical methods for the parameter estimation of gravitational wave signals from compact binary coalescence(CBC). Masses and spins of the black holes or the neutron stars are key parameters that determine the waveform of gravitational waves. However, their non-trivial correlation makes the MCMC process inefficient. We propose a technique using a new set of mass-spin sampling parameters which makes the posterior distribution to be simple in the new parameter space, regardless of the true value of the parameters. To achieve this, we use principal components of phase expansion coefficients of restricted 1.5 post-Newtonian(PN) waveform. Even the construction of the new parameters uses restricted PN waveform, our re-parameterization improves the efficiency of MCMC with another phenomenological waveform, by a factor of 10-1000. |
| Deep generative models of gravitational waveforms via conditional autoencoder | Chung-Hao Liao (Department of Physics, National Taiwan Normal University), Feng-Li Lin (Department of Physics, National Taiwan Normal University / Center of Astronomy and Gravitation, National Taiwan Normal University) | We construct few deep generative models of gravitational waveforms based on the semisupervising scheme of conditional autoencoders and its variational extensions. Once the training is done, we find that our best waveform model can generate the inspiral-merger waveforms of binary black hole coalescence with more than 97% average overlap matched filtering accuracy for the mass ratio between 1 and 10. Besides, the generation time of a single waveform takes about one millisecond, which is about 10 to 100 times faster than the EOBNR algorithm running on the same computing facility. Moreover, these models can also help to explore the space of waveforms. That is, with mainly the low-mass-ratio training set, the resultant trained model is capable of generating large amount of accurate high-mass-ratio waveforms. This result implies that our generative model can speed up the waveform generation for the low latency search of gravitational wave events. With improvement of the accuracy in the future work, the generative waveform model may also help to speed up the parameter estimation and can assist the numerical relativity in generating the waveforms of higher mass ratio by progressively self-training. |
| Optimizing Parameters of Information-Theoretic Correlation Measurement for Multi-Channel Time Series Datasets in Gravitational-Wave Detectors | Piljong Jung (NIMS), Sang Hoon Oh (NIMS), Young-Min Kim (UNIST), Edwin J. Son (NIMS), John J. Oh (NIMS) | Methodology for approximating the mutual information is presented with respect to its applicability to non-linear coupling estimation for two data sets described by the maximal information coefficient (MIC). The MIC is extended to measure associations between two variables and is employed in multi-channel data analysis in diverse fields of science and engineering. In this work, we investigate various prospects for determining optimized parameters of MIC to improve the reliability that deals with multi-channel time-series data and reduces massive computing costs in the viewpoint of practical usage. |
| Ten Questions for Gravitational Waves and Outlook | 중력파에 대한 10가지 질문을 통해 중력파 과학의 현재와 미래를 조망하고자 한다. 3차 관측가동이 종료된(2020년 3월 27일) 현재 총 50건의 중력파 검출이 발표되었다. 46건은 블랙홀 쌍성의 병합으로부터 발생한 중력파였고 나머지 4건은 중성자별이 관여되어 있거나 관여했을 가능성이 높다. 인류는 이러한 중력파의 직접 관측을 통해 100여년만에 중력파의 존재를 검증하였고, 매우 강한 중력장이나 광속의 약 70%에 달하는 영역에서도 일반상대론이 타당함을 검증하는 등 기념비적인 과학적 성취를 목도했다. 뿐만 아니라 중력파가 개입하는 천체현상을 이제는 관측의 영역에서 다룰 수 있는 소위 중력파 천문학 시대가 도래하였고 전통적인 전자기파나 중성미자와 같은 입자를 통한 관측과 협력하여 총체적으로 천체물리현상을 규명하는 다중신호 천문학이 형성되어 가고 있다. 이와 같이 매우 역동적으로 발전해 가는 중력파 과학에 대해 본 강연에서 그 현황을 정리하고 향 후 전망을 살펴보고자 한다. | |
| Searching for the Giants: Search for Intermediate Mass Black Holes in the 3rd Observing Run of Advanced LIGO-Virgo | Debnandini Mukherjee | Intermediate mass black holes (IMBHs) are known to have masses in the range of 100 to 100,000 solar masses and they make up the mass space between the stellar mass and the supermassive black holes. A direct, confirmed evidence of their observation has eluded us for long. In the 1st and the 2nd observing runs of LIGO-Virgo, no IMBHs were observed. GW190521, observed during the 3rd observing run, is the heaviest black hole binary coalescence seen yet by the LIGO-Virgo detectors, with its total mass being about 150 solar masses, consistent with an IMBH remnant. Observation rates of gravitational wave sources with at least one IMBH component, would help constrain their formation channel, which is uncertain at present. In my talk I will discuss the all-sky search for gravitational waves from IMBHs using modelled as well as model independent searches, during the 3rd observing of LIGO-Virgo. |
| The Gravitational-Wave Discoveries of Neutron Star - Black Hole Binary Mergers | Tanja Hinderer | Recently, the LIGO-Virgo-KAGRA collaboration announced the long-sought discoveries of gravitational waves from binary systems comprising (most likely) a neutron star and a black hole. I will start by discussing the fundamental physics of such mixed binary systems, then give an overview of the recent discoveries and their significance. I will conclude with an outlook onto the remaining challenges and interesting future prospects with such kinds of binary systems. |
| Observing neutron star-black hole binaries with gravitational waves | Leo Tsukada, LIGO-Virgo-KAGRA Collaboration | Compact binary systems of a neutron star paired with a black hole have long been predicted to form via a range of channels. However, unambiguous observation of these systems has remained elusive in gravitational-wave and electromagnetic surveys. I will discuss neutron star-black hole merger candidates in LIGO and Virgos third observing run, and discuss the prospects for future observations. |
| Measuring Hubble’s Constant with Signals from GW170817 Standard Siren and GW190814 Dark Siren | Rajesh Kumar Dubey (Lovely Professional University, India), Shankar Dayal Pathak (Lovely Professional University, India) | The local universe expansion rate is one of the most fundamental and essential cosmological parameters. This value which is known by the name of Hubble’s Constant is scientifically measured by electromagnetic sources called distance ladder. Surprisingly, using Gravitational Wave (GW) analysis this value can be measured making GW sources another significant method to act as standard sirens with their electromagnetic counterparts from their host galaxy. The gravitational wave event GW 170817 was the outcome of the merger of two different neutron stars. The electromagnetic event was recorded from the host galaxy NGC4993. The GW170817 has been a considerable success in this direction measuring the value of universe acceleration H0 = 70.0+12.0 −8.0 kms−1 Mpc−1 The results obtained from this GW event is analysed and compared with the other observations done with traditional methods of CMB and Cosmic Distance Ladder. Another event in this series GW190817 is Compact Binary Coalescence involving a 22.2 – 24.3 Solar Masses Blackhole and a compact object with a mass of 2.50 – 2.67 Solar Masses. The EM counterpart of this event is unknown so far and hence the event is named Dark Siren. The detection of gravitational waves from merger event GW190814 reveals a different picture. The Hubble’s value observed with this even is close to H0 = 75+59 −13 km s−1Mpc−1 .The source GW190814 which involves a massive black hole and the other compact object as the lightest black hole or the heaviest neutron star was localized to 18.5 deg2 at a distance of Mpc. The diversity of the two events can be used to measure the expansion rate of the universe. This can also be used to verify this rate in different directions of the universe. The results obtained from the two different types of Gravitational waves, originating from two different types of mergers gives two different results for a single cosmological parameter. This in addition to giving answer to the value of Hubble’s constant, also gives rise to Hubble’s tension. |
| Applications of Heun Functions and Regge Theory in Gravitational Wave Astrophysics | Aditya Tamar | The observations in of strong field gravity by current and future deployments of gravitational wave detectors has provided significant motivation to instrumentation, data analysis as well mathematical research to extract parameters of interest from observation. In this regard, mathematical astrophysics, utilising novel mathematical techniques to study and/or extract astrophysical data is expected to play a crucial role. The talk shall discuss two related areas of work and their impact on the broad field of gravitational wave astrophysics. Firstly, I shall discuss the astrophysical motivations and the utility to black hole perturbation theory of the recently formulated unconditionally convergent solutions of the class of Heun functions using the technique of path-sums, arising out of work with Pierre-Louis Giscard. The resultant formulation provides solutions in terms of a single elementary integral series representations of Heun functions, that is convergent from the black hole horizon upto spatial infinity. This significantly reduces the mathematical complexity in comparison to the well known Mano-Suzuki-Takesugi method that uses matched asymptotic expansions using parameters that don't exist in the Teukolsky equation and requires different functions for different spin of the black hole. In addition, I shall also discuss the utility of complex angular momentum and Regge theory techniques to studying astrophysical observables of Kerr black holes. This is part of ongoing work with Antoine Folacci wherein in a recent paper by Folacci and I, by using the Green's function for Teukolsky equation, Regge theory has been shown to be remarkably effective in producing quasinormal mode frequencies for almost entire parameter range relevant for gravitational wave physics. I shall also describe the utility of Heun functions to Regge theory as well. For other astrophysical applications of the Teukolsky equation such as computing gravitational wave fluxes, I shall discuss how a uniformly convergent Heun function can resolve mathematical bottlenecks arising from divergent series summations of spin weighted spheroidal harmonics and long range potentials (the latter being currently addressed using the Saski-Nakamura transform) and discuss the prospects of a unified formalism for black hole perturbation theory based solely on the Heun functions |
| Light perturbation and detection of gravitational waves via pulsar timing arrays | Dong-Hoon Kim (Seoul National University), Chan Park (National Institute for Mathematical Sciences) | Light undergoes perturbation as gravitational waves pass by. This is shown by solving Maxwell's equations in a spacetime with gravitational waves; a solution exhibits a perturbation due to gravitational waves. We determine the perturbation for a general case of both light and gravitational waves propagating in arbitrary directions. It is also shown that a perturbation of light due to gravitational waves leads to a delay of the photon transit time, which implies an equivalence between the perturbation analysis of Maxwell's equations and the null geodesic analysis for photon propagation. We present an example of application of this principle with regard to the detection of gravitational waves via a pulsar timing array, wherein our perturbation analysis for the general case is employed to show how the detector response varies with the incident angle of a light pulse with respect to the detector. |
| Gravitational-wave constraints on GWTC-2 events by measuring tidal deformability and spin-induced quadrupole moment | Tatsuya Narikawa (ICRR), Nami Uchikata (ICRR), Takahiro Tanaka (Kyoto U) | Gravitational waves from compact binary coalescences provide a unique laboratory to test properties of compact objects. As alternatives to the ordinary black holes in general relativity, various exotic compact objects have been proposed. Some of them have largely different values of the tidal deformability and spin-induced quadrupole moment from those of black holes, and their binaries could be distinguished from binary black hole by using gravitational waves emitted during their inspiral regime, excluding the highly model-dependent merger and ring-down regimes. We reanalyze gravitational waves from low-mass merger events in the GWTC-2 catalog, detected by Advanced LIGO and Advanced Virgo. Focusing on the influence of tidal deformability and spin-induced quadrupole moment in the inspiral waveform, we provide model-independent constrains on deviations from the standard binary black hole case. We find that all events that we have analyzed are consistent with the waveform of binary black hole in general relativity. Bayesian model selection shows that the hypothesis that the binary is composed of exotic compact objects is disfavored by all events. |
| Search sensitivity for gravitational waves from black hole capture events | Michael Ebersold (University of Zurich), Leigh Smith (University of Glasgow), Shubhanshu Tiwari (University of Zurich), Daniel Williams (University of Glasgow), Maria Haney (University of Zurich), Ik Siong Heng (University of Glasgow), Yeong-Bok Bae (NIMS Daejeon), Gungwon Kang (Chung-Ang University Seoul) | Though the majority of observed gravitational wave signals will be from circularized binary black hole systems, a fraction of black hole mergers will have significant eccentricities, for example, due to radiation driven capture. Using waveforms from numerical relativity simulations we show that radiation driven capture of stellar mass black holes are detectable within the sensitivity band of current detectors using non-template based searches such as coherent WaveBurst. We present the results of a study on the search sensitivity of these events in data from the second observing run of LIGO-VIRGO, and discuss future prospects for observing gravitational waves from direct capture events. |
| Small-scale shear: peeling off diffuse subhalos with gravitational waves | Han Gil Choi, Chanung Park, Sunghoon Jung | Subhalos at subgalactic scales (M≲10^7 Msun or k≳10^3 Mpc^−1) are pristine testbeds of dark matter (DM). However, they are too small, diffuse and dark to be visible, in any existing observations. In this paper, we develop a complete formalism for weak and strong diffractive lensing, which can be used to probe such subhalos with chirping gravitational waves (GWs). Also, we show that NFW subhalos in this mass range can indeed be detected individually, albeit at a rate of O(10) or less per year at BBO and others limited by small merger rates and large required SNR ≳1/γ(r0)∼10^3. It becomes possible as NFW scale radii r0 are of the right size comparable to the GW Fresnel length rF, and unlike all existing probes, their lensing is more sensitive to lighter subhalos. Further remarkably, our formalism reveals that the frequency dependence of weak lensing, what is actually the detectable effect, is due to shear γ at rF. Not only is it consistent with an approximate scaling invariance, but it also offers a new way to measure the mass profile at a successively smaller scale of chirping rF∝f^−1/2. Meanwhile, strong diffraction that produces a blurred Einstein ring rather has a universal frequency dependence, allowing only detections. These are further demonstrated through semi-analytic discussions of power-law profiles. Our developments for a single lens can be generalized and will promote diffractive lensing to a more concrete and promising physics in probing DM and small-scale structures. |
| Ponderomotive Squeezing R&D with SIPS | Luca Naticchioni | In present and future Gravitational Wave Detectors the quantum noise mitigation is crucial and it is achieved through the injection of squeezed states of the light in the interferometer. Currently the well established squeezing technique is that based on an OPO source plus a filter cavity to achieve a frequency-dependent squeezing. The ponderomotive effect is a promising alternative to create correlations between phase and amplitude of an EM field inside an optical cavity with suspended mirrors. The SIPS interferometer is a small-scale experiment to demonstrate the feasibility of this technique, moreover this radiation-pressure-limited interferomter will be used as demonstrator of another novel squeezing technique based on the EPR entanglement. In this talk I will show the main features and the current status of this project. |
| Atomic Structure Characterization Research to Find Prospective Coating Materials for GW Detectors | Kyung-Ha Lee | Since the first detection, gravitational wave research communities around the world put focus on improving the detectors’ sensitivity to detect more signals from various astronomical sources. Among many noise sources in the gravitational wave detectors, coating Brownian noise arose as one of the most critical limiting factor, since recent upgrade plans have significantly decreased the quantum noise. Empirical optimization can no longer be the solution, thus a new research model has been setup. This new approach utilizes atomic structure study to find a low loss material, and we successfully found a new potential coating for the A+LIGO. This research model with atomic structure study is also applicable for other gravitational wave research in general, such as cryogenic conditions. In today’s talk, I will introduce this new research model and present the A+LIGO’s case as a successful example. |
| Prospects for Routine Observations of Intermediate-Mass Black Holes with Gravitational-Wave Observatories | Denis Martynov | The discoveries made by the LIGO and Virgo detectors have had a transformative impact on astronomy and astrophysics. Taking full advantage of the gravitational-wave window requires even better detectors that can survey the Universe on its largest scales and provide information of broad interest in astrophysics, cosmology, and nuclear physics. In this talk, I will discuss new seismic isolation technology that can help LIGO routinely observe intermediate-mass black holes. I will show how the developments made in the other fields, including space detectors and compact interferometers, can boost the LIGO low frequency sensitivity in the future. |
| Extract the Degradation Information in Squeezed States with Machine Learning | Yi-Ru Chen (National Tsing Hua University), Hsien-Yi Hsieh (National Tsing Hua University), Hsun-Chung Wu (National Tsing Hua University), Huali Chen (National Tsing Hua University), Yao-Chin Huang (National Tsing Hua University), Chien-Ming Wu (National Tsing Hua University), and Ray-Kuang Lee (National Tsing Hua University) | Squeezed states have been widely applied to the advanced gravitational wave detectors, quantum metrology, macroscopic quantum state generation, and quantum information process. In order to leverage the full power of quantum noise squeezing with unavoidable decoherence, a complete understanding on the degradation in the purity of squeezed light is demanded. By implementing machine learning architecture with a convolutional neural network, we illustrate a fast, robust, and precise quantum state tomography for continuous variables, through the experimentally measured data generated from the balanced homodyne detectors. Compared with the maximum likelihood estimation method, which suffers from time consuming and over-fitting problems, a well-trained machine fed with squeezed vacuum and squeezed thermal states can complete the task on the reconstruction of density matrix in less than one second. Compared with the phase noise and loss mechanisms coupled from the environment and surrounding vacuum, experimentally, the degradation information is unveiled with machine learning for low and high noisy scenarios, i.e., with the anti-squeezing levels at 12 dB and 18 dB, respectively. |
| High resolution microcantilever based loss angle measurements for quarter wavelength and nanolayered coating research | Richard Pedurand (INFN) | The ultimate visibility distance of ground based Gravitational Wave Detectors (GWD) like Advanced LIGO, Advanced Virgo, and KAGRA is limited by the brownian thermal noise of their mirrors. Among other factors, this noise is proportional to the mirrors' temperature and the mechanical dissipation occurring inside their reflective coating materials, according to the fluctuation-dissipation theorem. KAGRA is the first operational GWD employing cryocooled mirrors as a mean to mitigate coating thermal noise. As a result, an important research effort has been devoted to the development of coating materials exhibiting excellent optical properties as well as a very low level of mechanical dissipation, at both room and cryogenic temperatures. In this regard, several instrumental setups have been developed to measure the mechanical dissipation or directly the power spectral density of thermal fluctuations in optical thin films. During my PhD thesis at the LMA, from 2015 to 2018, I built the CryoQPDI, a new instrument to perform direct thermal noise measurement on coated, micron-sized cantilevers. The microcantilever is placed inside a closed cycle cryostat and its brownian motion is monitored using a high-resolution Quadrature Phase Differential Interferometer (QPDI). I recently earned a position in the USannio/UniSA Coating Research Group (a member of the Virgo VCRD and the LIGO OWG), where I plan to exploit this concept for further coating material studies. I plan to focus on the development of nanolayered coating, which have been found to suppress the low temperature loss angle peak exhibited by classic quarter-wavelength layers. During this talk, I will briefly explain the working principle of the QPDI for microcantilever based measurements, as well as its advantages compared to the GeNS setup and the MIT CTN instrument. I will present cryogenic measurement on undoped tantala films as a proof of the concept. Finally, I will discuss why the QPDI is particularly relevant for the study of nanolayered coating materials, and some related future research lines that could be explored. |
| Rapid Parameter Estimation of Gravitational Waves from Compact Binary Coalescence | Soichiro Morisaki (University of Wisconsin-Milwaukee) | Bayesian parameter estimation of gravitational waves from compact binary coalescence plays an important role in the era of gravitational-wave astronomy. On the other hand, it is computationally costly because it requires millions of evaluations of computationally expensive template waveforms. In this talk, I will introduce two techniques to reduce its cost: Focused Reduced Order Quadrature (FROQ) and Multi-banding. FROQ optimizes the likelihood evaluations based on rough estimates of source parameters available at the detection of signal. It speeds up the parameter estimation of binary neutron star signal by a factor of O(10^4), and reduces the run time from more than a few weeks to tens of minutes. On the other hand, the multi-banding method is not as fast as FROQ. However, it does not require any offline preparations or accurate estimates of source parameters, and more easy-to-use. These techniques are complementary and useful in analyses from low-latency sky localization to accurate estimates of source parameters. |
| GPE: GPU-accelerated Parameter Estimation for Gravitational Waves | Yun-Jing Huang (Academia Sinica, Taiwan), Sadakazu Haino (Academia Sinica, Taiwan) | We present GPE, a GPU-accelerated parameter estimation package for gravitational waves from compact binary coalescence sources. This stand-alone program is adapted from the nested sampling flavor of LALInference. Two main parallelization methods are implemented: (1) the frequency-domain waveform and likelihood calculations, (2) and the prior sampling portion in the nested sampling algorithm. We show that GPE can produce consistent results compared to LALInference, while demonstrating a 300-400 times speedup on one GPU compared to LALInference on one CPU. The high acceleration of GPE can facilitate the data-analysis of detected events, simulations for detector observing scenarios, and production of sky localization regions for EM follow-up. |
| Searching gravitational wave signal with autoregressive approach | Hui, David C. Y. (Chungnam National University), Lin, Lupin (UNIST), Kong , Albert (NTHU), Shinkai, Hisaaki (OIT), Li, K.L. (NCKU), Oh, Kwangmin (Chungnam National University), Kim, Sangin (Chungnam National University), Yan, J.Q. (MUST), Leung, Alex (MUST), Luo, Shengda (MUST) | We are developing a novel framework of searching gravitational wave signal by coupling the stochastic autoregressive modeling. This proposed framework holds the potential for an automatic pipeline for noise reduction, event candidate detections and template-free parameter estimation. Currently, we are testing the method with LIGO O1/O2 data. |
| Searching for signals from ultralight vector dark matter with KAGRA | Yuta Michimura | Recently, a considerable amount of attention has been given to the search for ultralight dark matter by measuring the oscillating length changes in the arm cavities of gravitational wave detectors. Although gravitational wave detectors are extremely sensitive for measuring the differential arm length changes, the sensitivity to dark matter is largely attenuated, as the effect of dark matter is mostly common to arm cavity test masses. In PRD 102, 102001 (2020), we have proposed to use auxiliary length channels, which measure the changes in the power and signal recycling cavity lengths and the differential Michelson interferometer length. The sensitivity to dark matter can be enhanced by exploiting the fact that auxiliary interferometers are more asymmetric than two arm cavities. We have shown that the sensitivity to U(1)_{B−L} gauge boson dark matter in the low mass region can be greatly enhanced when our method is applied to a cryogenic gravitational wave detector KAGRA, which employs sapphire test masses and fused silica auxiliary mirrors. We have shown that KAGRA can probe more than an order of magnitude of unexplored parameter space at masses around 1.5×10^{−14} eV, without any modifications to the existing interferometer. In this talk, we present the current status of the data analysis pipeline development, and discuss the prospects of our analysis using KAGRA data from O3GK observing run. |
| Ensemble Empirical Mode Decomposition Applied to Reconstruction of Core-Collapse Supernovae Gravitational-Waves Waveforms | Yong Yuan, Xi-Long Fan, Hou-Jun Lv, Yu-Feng Li | The gravitational waves from core-collapse supernovae(CCSN) have been proposed as a probe to investigate physical properties inside the supernova. However, how to search and extract the gravitational wave (GW) signals from core-collapse supernovae remains an open question due to its complicated time-frequency structure. In this paper, we proposed Ensemble Empirical Mode Decomposition (EEMD) which can break the signal down into many intrinsic mode functions (IMFs) over a range from high frequency to low frequency, and it could be applied to extract and re-construct the GW signals as detected by Advanced LIGO at designated sensitivity with added Gaussian noise. We also used match score to evaluate how many IMFs are needed to represent the reconstructed signal, and set a match score threshold of 0.8 as a criterion to explore the largest detectable distances via this method. Moreover, we also discussed that the probability of the reconstructed signal is belonging to the noise. We determine that those reconstructed signals could be detected rather than noise when the match score is larger than 0.8. Our result shows that the sum of the first six IMFs from the extracted signal is necessary to reconstruct signal. We can reconstruct gravitational-wave signals by assuming the strain of 10−22 within the distance of 5 kpc, and the GW signals at a farther distance can be reached if the amplitude is stronger enough. |
| Exploring gravitational-wave detection and parameter inference using deep learning | He Wang (ITP-CAS), Zhoujian Cao (BNU), Haiyu Fu (PCL), ZongKuan Guo (ITP-CAS), Zhixiang Ren (PCL) | The LIGO and Virgo gravitational-wave (GW) observatories have detected many exciting events over the past five years. As the rate of detections grows with detector sensitivity, this poses a growing computational challenge for data analysis. Based on this, we review how machine learning can enhance GW detection and parameter estimation. By training with the detector noise power spectral density estimated at the time of GW events and conditioning on the information of event strain data, we demonstrate that the deep learning technique constitutes an attractive choice to speed up classification and generate accurate posterior samples consistent with analyses in GWTC-1. |
| Status of KAGRA DET | Takahiro Yamamoto (ICRR) on behalf of the KAGRA collaboration | KAGRA performed the observing run in April 2020 called O3GK, and DetChar group evaluated the quality of observational data and shared them among LVK. Currently, commissioning tests are being conducted in parallel with the hardware upgrade of the interferometer. In this talk, I will give a summary of the data quality evaluation in O3GK, improvements toward O4, and activities in O4 commissioning. |
| Noise hunting during KAGRA commissioning | Hirotaka Yuzurihara | Now KAGRA is in the phase of commissioning to improve the sensitivity to join O4 observation run. The unknown correlation between PMC and microphones has been reported during the commissioning. The investigation to reveal the noise contamination path are on-going. In this talk, I will give a presentation about the recent activities of noise hunting on the commissioning. |
| Optimizing Parameters of Information-Theoretic Correlation Measurement for Multi-Channel Time Series Datasets in Gravitational-Wave Detectors | Piljong Jung (NIMS), Sang Hoon Oh (NIMS), Young-Min Kim (UNIST), Edwin J. Son (NIMS), John J. Oh (NIMS) | Methodology for approximating the mutual information is presented with respect to its applicability to non-linear coupling estimation for two data sets described by the maximal information coefficient (MIC). The MIC is extended to measure associations between two variables and is employed in multi-channel data analysis in diverse fields of science and engineering. In this work, we investigate various prospects for determining optimized parameters of MIC to improve the reliability that deals with multi-channel time-series data and reduces massive computing costs in the viewpoint of practical usage. |
| Introduction to Computing Environments at KISTI-GSDC LDG | Global Science experimental Data hub Center (GSDC) at Korea Institute of Science and Technology Information (KISTI) is a datacenter that was built by a national funding project to promote fundamental research activities in South Korea. GSDC is currently serving as Asia's leading data center following changes in the new research paradigm and supports experiments such as ALICE, CMS, LIGO/KAGRA, Belle2, RENO, Genome Projects, etc. In particular, we have recently upgraded existing GSDC-LIGO data grid (LDG) tier 3 systems to tier 2 services due to increased computing demands from LIGO/KAGRA groups. In this presentation, I will introduce KISTI-GSDC, and explain the history and status of GSDC-LDG system. | |
| Status of the ET Project | Michele Punturo | The Einstein Telescope project is entering in a crucial phase: a group of European countries and research institutions supported the submission of the ET proposal to the European roadmap for the future large infrastructures (ESFRI), the ET collaboration is under formalisation and the activities addressed to the realisation of the observatory are accelerating. The status of the project will be presented. |
| Prospects for observing multiple quasinormal modes with gravitational wave detectors | Iara Ota (Federal University of ABC), Cecilia Chirenti (University of Maryland College Park, NASA GSFC, Federal University of ABC) | The waveform emitted during the final stage of a binary black hole merger is described by the quasinormal modes of the remnant black hole, whose frequencies and damping times are characterized by its mass and spin. With the observation of multiple quasinormal modes an independent test can be performed to check whether the source is compatible with a Kerr black hole, and this is known as black hole spectroscopy. For nonspinning circular black hole binaries, we obtain the black hole spectroscopy horizons: the maximum distance up to which two or more quasinormal modes can be detected. We find that the first overtone of the quadrupolar mode is favored over the higher harmonics for more symmetric initial masses and the higher harmonics have larger horizons for less symmetric initial masses. |
| Second order measurements in interferometric gravitational wave detectors | Chan Park(NIMS) | Interferometric gravitational wave detectors observe gravitational waves through dark port intensity of the interferometer. Existing analyses on interferometers are usually given in first order phase difference between two arms. We would like to provide measurements which contain second order effect in the phase difference, and show its analytic expectation when gravitational wave is passing. |
| Advanced configurations for a high-frequency GW measurement | Kentaro Somiya | There have been some ideas to improve the detector sensitivity at 3-4kHz aiming at an observation of a neutron star binary coalescence. I would like to review those techniques (extreme RSE, long SRC, parametric amplification, quantum expander, white light cavity, etc.) and promote discussions toward a future upgrade of KAGRA. |
| Instrumented baffles for AdV+ | M. Martinez | As part of the upgrade program, Virgo has just installed a new baffle equipped with photosensors that surrounds the end-mirror of the input mode-cleaner. This culminates more than two years of work at IFAE-Barcelona for the design and construction of a novel and innovative device to control and monitor stray light inside the experiment, a persistent source of noise in interferometers. It will serve as a demonstrator of the technology for its future implementation in the main arms of the interferometer, surrounding the test masses. The new baffle will provide valuable data for understanding the cavity and calibrating simulations that describe the propagation of light within the interferometer. The instrumented baffle is now entering a long period of commissioning and integration into Virgo's regular operations, in time to become an integral part of the new O4 observation run, currently scheduled for summer 2022. In this talk we describe the technology and we present the first results of its performance within the experiment. |
| Investigating thermal noise in gram-scale silicon flexures at 123 K | Johannes Eichholz (ANU), Disha Kapasi (ANU), Terry McRae (ANU), Paul Altin (ANU), Bram Slagmolen (ANU), David McClelland (ANU) | Cryogenically cooled silicon test masses and suspensions are a strong prospect for the future of ground-based gravitational wave detection. A silicon-based monolithic suspension stage would likely profit from using a flattened ribbon geometry to increase flexibility in the primary longitudinal arm cavity degree of freedom. At the Australian National University, we study the thermal noise of gram-scale silicon cantilevers which dimensionally resemble such silicon ribbons. We isolate the cantilevers using a multi-stage torsion pendulum and measure their off-resonant thermal noise directly with cavity-enhanced interferometric readout. We are currently upgrading our vacuum chamber with a cryocooler and shielding to radiatively cool our cantilever samples to 123 K. I will present initial cooldown results, the latest status of direct thermal noise measurements, and future plans. |
| Thermal noise of a silicon micro-cantilever submitted to a temperature contrast over one hundred | Alex Fontana (Institut Néel, Université Grenoble Alpes, France), Richard Pedurand (University of Sannio at Benevento, INFN, Italy), Vincent Dolique (ENS of Lyon, Laboratoire de Physique, UCBL1, CNRS, France), Ghaouti Hansali (ENISE, France), Ludovic Bellon (ENS of Lyon, Laboratoire de Physique, UCBL1, CNRS, France) | Thermal noise of a silicon micro-cantilever submitted to a temperature contrast over one hundred Thermal noise manifests itself as a tiny variance around the mean value of an observable x of a physical system. Usually too small to be noticed, it becomes important in an increasing number of applications, such as quantum systems operated close to their ground state, MEMS and NEMS, frequency standards, or the next generation of gravitational wave detectors [1]. In this last field, experiments are sometimes performed at cryogenic temperatures in order to facilitate the measurements, for example in KAGRA [2]. The understanding of thermal noise in these extreme conditions is thus fundamental. k_B T_fluc = k ⟨x^2⟩ with k_B the Boltzmann constant, k the stiffness, and ⟨x^2⟩ the variance of the observable, i.e. the thermal noise. As in the previous experiments [3, 4], we demonstrate that the system shows a strong lack of fluctuations with respect to what its average temperature Tavg dictates [5]. Indeed, the cantilever’s thermal noise amplitude is close to what would be expected from the lowest temperature of the system for any temperature imposed at its free end. Thanks to a simultaneous estimation of the dissipation of the system, we give a theoretical interpretation of our findings. These results can be useful to understand the non-equilibrium behavior of thermal noise at low temperature of silicon, which is also a candidate material for future gravitational wave detectors [6]. -------- [1] G. M. Harry, H. Armandula, E. Black, D. R. M. Crooks, G. Cagnoli, J. Hough, P. Murray, S. Reid, S. Rowan, P. Sneddon, M. M. Fejer, R. Route, and S. D. Penn, Thermal noise from optical coatings in gravitational wave detectors, Appl. Opt. 45, 1569 (2006). |
| Optimized Ternary Coatings : Design and Performance | Innocenzo M. Pinto (University of Naples, INfN, LVK and Centro Fermi); Vincenzo Pierro (University of Sannio dt Benevento) | The structure of 3-material coatings featuring the lowest thermal noise under prescribed transmittance and absorbance constraints is investigated and revealed. The performance of ternary optimized coatings based on different materials, including amorphous Silicon or Silicon Nitride in addition to Ti-doped Tantala and Silica is discussed and compared with alternative options, for operation at ambient and cryogenic temperatures. |
Overview
Content Tools