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

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

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

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

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

Constraining Black Hole Populations in Globular Clusters using Microlensing: Application to Omega Centauri

We estimate the rate of gravitational microlensing events of cluster stars due to black holes (BHs) in the globular cluster NGC 5139 ($\omega Cen$). Theory and observations both indicate that $\omega Cen$ may contain thousands of BHs, but their mass spectrum and exact distribution are not well constrained. In this Letter we show that one may observe microlensing events on a timescale of years in $\omega Cen$, and such an event sample can be used to infer the BH distribution. Direct detection of BHs will, in the near future, play a major role in distinguishing binary BH merger channels. Here we explore how gravitational microlensing can be used to put constraints on BH populations in globular clusters.Comment: 6 pages, 2 figures, published in ApJ