The Advanced LIGO timing system

Gravitational wave detection using a network of detectors relies upon the precise time stamping of gravitational wave signals. The relative arrival times between detectors are crucial, e.g. in recovering the source direction, an essential step in using gravitational waves for multi-messenger astronomy. Due to the large size of gravitational wave detectors, timing at different parts of a given detector also needs to be highly synchronized. In general, the requirement toward the precision of timing is determined such that, upon detection, the deduced (astro-) physical results should not be limited by the precision of timing. The Advanced LIGO optical timing distribution system is designed to provide UTC-synchronized timing information for the Advanced LIGO detectors that satisfies the above criterium. The Advanced LIGO timing system has modular structure, enabling quick and easy adaptation to the detector frame as well as possible changes or additions of components. It also includes a self-diagnostics system that enables the remote monitoring of the status of timing. After the description of the Advanced LIGO timing system, several tests are presented that demonstrate its precision and robustness

Merits of coincident observation of energetic cosmic events by astronomical and gravity wave observatories

Presently there are six interferometric gravitational wave detectors in the commissioning or construction phase in North America, Europe, and Japan. Once completed this worldwide network of detectors will be capable of detecting gravitational waves with unprecedented detail and sensitivity. Their ambition reaches well beyond the first direct detection of gravitational waves; they promise the dawn of a new field, the gravitational wave astronomy. One of the major goals of interferometric gravity wave detectors is to develop and exploit gravitational wave detection in conjunction with other conventional observational techniques, which are capable of observing the same astronomical process using different methods. The most promising areas are the optical, GRB and neutrino searches for energetic processes. Coincident observation of astronomical events shall revolutionize the way we understand energetic processes and will provide a new window on compact and difficult to study astronomical objects such as stellar cores. We will discuss the status, the potential future, and benefits of collaboration amongst gravitational wave detector networks and astronomical/GRB/neutrino networks and some of the practical experiences with the LIGO detectors

Rapid and Bright Stellar-mass Binary Black Hole Mergers in Active Galactic Nuclei

The Laser Interferometer Gravitational-Wave Observatory, LIGO, found direct evidence for double black hole binaries emitting gravitational waves. Galactic nuclei are expected to harbor the densest population of stellar-mass black holes. A significant fraction ($\sim30\%$) of these black holes can reside in binaries. We examine the fate of the black hole binaries in active galactic nuclei, which get trapped in the inner region of the accretion disk around the central supermassive black hole. We show that binary black holes can migrate into and then rapidly merge within the disk well within a Salpeter time. The binaries may also accrete a significant amount of gas from the disk, well above the Eddington rate. This could lead to detectable X-ray or gamma-ray emission, but would require hyper-Eddington accretion with a few percent radiative efficiency, comparable to thin disks. We discuss implications for gravitational wave observations and black hole population studies. We estimate that Advanced LIGO may detect $\sim20$ such, gas-induced binary mergers per year.Comment: 9 pages, 2 figure

Opportunity to Test non-Newtonian Gravity Using Interferometric Sensors with Dynamic Gravity Field Generators

We present an experimental opportunity for the future to measure possible violations to Newton's 1/r^2 law in the 0.1-10 meter range using Dynamic gravity Field Generators (DFG) and taking advantage of the exceptional sensitivity of modern interferometric techniques. The placement of a DFG in proximity to one of the interferometer's suspended test masses generates a change in the local gravitational field that can be measured at a high signal to noise ratio. The use of multiple DFGs in a null experiment configuration allows to test composition independent non-Newtonian gravity significantly beyond the present limits. Advanced and third-generation gravitational-wave detectors are representing the state-of-the-art in interferometric distance measurement today, therefore we illustrate the method through their sensitivity to emphasize the possible scientific reach. Nevertheless, it is expected that due to the technical details of gravitational-wave detectors, DFGs shall likely require dedicated custom configured interferometry. However, the sensitivity measure we derive is a solid baseline indicating that it is feasible to consider probing orders of magnitude into the pristine parameter well beyond the present experimental limits significantly cutting into the theoretical parameter space.Comment: 9 pages, 6 figures; Physical Review D, vol. 84, Issue 8, id. 08200

Observational Constraints on Multi-messenger Sources of Gravitational Waves and High-energy Neutrinos

It remains an open question to what extent many of the astronomical sources of intense bursts of electromagnetic radiation are also strong emitters of non-photon messengers, in particular gravitational waves (GWs) and high-energy neutrinos (HENs). Such emission would provide unique insights into the physics of the bursts; moreover some suspected classes, e.g. choked gamma-ray bursts, may in fact only be identifiable via these alternative channels. Here we explore the reach of current and planned experiments to address this question. We derive constraints on the rate of GW and HEN bursts per Milky Way equivalent (MWE) galaxy based on independent observations by the initial LIGO and Virgo GW detectors and the partially completed IceCube (40-string) HEN detector. We take into account the blue-luminosity-weighted distribution of nearby galaxies, assuming that source distribution follows the blue-luminosity distribution. We then estimate the reach of joint GW+HEN searches using advanced GW detectors and the completed cubic-km IceCube detector to probe the joint parameter space. We show that searches undertaken by advanced detectors will be capable of detecting, constraining or excluding, several existing models with one year of observation

Gamma-ray burst precursors from tidally resonant neutron star oceans: potential implications for GRB 211211A

Precursor emission has been observed seconds to minutes before some short gamma-ray bursts. While the origins of these precursors remain unknown, one potential explanation relies on the resonance of neutron star pulsational modes with the tidal forces during the inspiral phase of a compact binary merger. In this paper, we present a model for short gamma-ray burst precursors which relies on tidally resonant neutron star oceans. In this scenario, the onset of tidal resonance in the crust-ocean interface mode corresponds to the ignition of the precursor flare, possibly through the interaction between the excited neutron star ocean and the surface magnetic fields. From just the precursor total energy, the time before the main event, and a detected quasi-periodic oscillation frequency, we may constrain the binary parameters and neutron star ocean properties as never before. Our model can immediately distinguish neutron star-black hole mergers from binary neutron star mergers without gravitational wave detection. We apply our model to GRB 211211A, the recently detected long duration short gamma-ray burst with a quasi-periodic precursor, and explore the parameters of this system within its context. The precursor of GRB 211211A is consistent with a tidally resonant neutron star ocean explanation that requires an extreme-mass ratio NSBH merger and a high mass neutron star. While difficult to reconcile with the gamma-ray burst main emission and associated kilonova, our results constrain the possible precursor generating mechanisms in this system. A systematic study of short gamma-ray burst precursors with the model presented here can test precursor origin and could probe the possible connection between gamma-ray bursts and neutron star-black hole mergers.Comment: 9 pages, 2 figures, accepted in MNRA

Boosting the Efficiency of Parametric Detection with Hierarchical Neural Networks

Gravitational wave astronomy is a vibrant field that leverages both classic and modern data processing techniques for the understanding of the universe. Various approaches have been proposed for improving the efficiency of the detection scheme, with hierarchical matched filtering being an important strategy. Meanwhile, deep learning methods have recently demonstrated both consistency with matched filtering methods and remarkable statistical performance. In this work, we propose Hierarchical Detection Network (HDN), a novel approach to efficient detection that combines ideas from hierarchical matching and deep learning. The network is trained using a novel loss function, which encodes simultaneously the goals of statistical accuracy and efficiency. We discuss the source of complexity reduction of the proposed model, and describe a general recipe for initialization with each layer specializing in different regions. We demonstrate the performance of HDN with experiments using open LIGO data and synthetic injections, and observe with two-layer models a $79\%$ efficiency gain compared with matched filtering at an equal error rate of $0.2\%$. Furthermore, we show how training a three-layer HDN initialized using two-layer model can further boost both accuracy and efficiency, highlighting the power of multiple simple layers in efficient detection