Distributed State Machine Supervision for Long-baseline Gravitational-wave Detectors

The Laser Interferometer Gravitational-wave Observatory (LIGO) consists of two identical yet independent, widely-separated, long-baseline gravitational-wave detectors. Each Advanced LIGO detector consists of complex optical-mechanical systems isolated from the ground by multiple layers of active seismic isolation, all controlled by hundreds of fast, digital, feedback control systems. This article describes a novel state machine-based automation platform developed to handle the automation and supervisory control challenges of these detectors. The platform, called \textit{Guardian}, consists of distributed, independent, state machine automaton nodes organized hierarchically for full detector control. User code is written in standard Python and the platform is designed to facilitate the fast-paced development process associated with commissioning the complicated Advanced LIGO instruments. While developed specifically for the Advanced LIGO detectors, Guardian is a generic state machine automation platform that is useful for experimental control at all levels, from simple table-top setups to large-scale multi-million dollar facilities.Comment: Version 2: 11 pages, 9 figures. Submitted to Review of Scientific Instrument

Implementation and testing of the first prompt search for gravitational wave transients with electromagnetic counterparts

Aims. A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM follow-ups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations. Methods. During two observing periods (Dec 17 2009 to Jan 8 2010 and Sep 2 to Oct 20 2010), a low-latency analysis pipeline was used to identify GW event candidates and to reconstruct maps of possible sky locations. A catalog of nearby galaxies and Milky Way globular clusters was used to select the most promising sky positions to be imaged, and this directional information was delivered to EM observatories with time lags of about thirty minutes. A Monte Carlo simulation has been used to evaluate the low-latency GW pipeline's ability to reconstruct source positions correctly. Results. For signals near the detection threshold, our low-latency algorithms often localized simulated GW burst signals to tens of square degrees, while neutron star/neutron star inspirals and neutron star/black hole inspirals were localized to a few hundred square degrees. Localization precision improves for moderately stronger signals. The correct sky location of signals well above threshold and originating from nearby galaxies may be observed with ~50% or better probability with a few pointings of wide-field telescopes.Comment: 17 pages. This version (v2) includes two tables and 1 section not included in v1. Accepted for publication in Astronomy & Astrophysic

A Virtual Data Grid for LIGO

GriPhyN (Grid Physics Network) is a large US collaboration to build grid services for large physics experiments, one of which is LIGO, a gravitational-wave observatory. This paper explains the physics and computing challenges of LIGO, and the tools that GriPhyN will build to address them. A key component needed to implement the data pipeline is a virtual data service; a system to dynamically create data products requested during the various stages. The data could possibly be already processed in a certain way, it may be in a file on a storage system, it may be cached, or it may need to be created through computation. The full elaboration of this system will al-low complex data pipelines to be set up as virtual data objects, with existing data being transformed in diverse ways

Status of LIGO

LIGO construction has been completed. The three interferometers at the two LIGO observatory sites (Livingston, Louisiana and Hanford, Washington) have been operated successfully as power-recycled Michelson interferometers with Fabry-Perot arm cavities. Commissioning of the interferometers has progressed to operating them simultaneously in this final optical configuration. The initial coincidence operation between the observatory sites has provided a full test of the detector hardware and software subsystems, and full operation of the data acquisition and data analysis systems. The LIGO Laboratory and the LIGO Scientific Collaboration are working together to exploit the early series of interleaved engineering and science runs to commission the detector and data systems, to provide a detailed characterization of the detector and to produce the first scientific results from LIGO. The operation of LIGO is also coordinated with operation of the GEO 600 detector and the ALLEGRO resonant mass detector. The status of this early operation and data study will be presented