M. Was

X-Pipeline: an analysis package for autonomous gravitational-wave burst searches

Autonomous gravitational-wave searches—fully automated analyses of data that run without human intervention or assistance—are desirable for a number of reasons. They are necessary for the rapid identification of gravitational-wave burst candidates, which in turn will allow for follow-up observations by other observatories and the maximum exploitation of their scientific potential. A fully automated analysis would also circumvent the traditional by hand setup and tuning of burst searches that is both labourious and time consuming. We demonstrate a fully automated search with X-Pipeline, a software package for the coherent analysis of data from networks of interferometers for detecting bursts associated with gamma-ray bursts (GRBs) and other astrophysical triggers. We discuss the methods X-Pipeline uses for automated running, including background estimation, efficiency studies, unbiased optimal tuning of search thresholds and prediction of upper limits. These are all done automatically via Monte Carlo with multiple independent data samples and without requiring human intervention. As a demonstration of the power of this approach, we apply X-Pipeline to LIGO data to compute the sensitivity to gravitational-wave emission associated with GRB 031108. We find that X-Pipeline is sensitive to signals approximately a factor of 2 weaker in amplitude than those detectable by the cross-correlation technique used in LIGO searches to date. We conclude with comments on the status of X-Pipeline as a fully autonomous, near-real-time-triggered burst search in the current LSC-Virgo Science Run.

The transient gravitational-wave sky

Interferometric detectors will very soon give us an unprecedented view of the gravitational-wave sky, and in particular of the explosive and transient Universe. Now is the time to challenge our theoretical understanding of short-duration gravitational-wave signatures from cataclysmic events, their connection to more traditional electromagnetic and particle astrophysics, and the data analysis techniques that will make the observations a reality. This paper summarizes the state of the art, future science opportunities, and current challenges in understanding gravitational-wave transients.

Performance of an externally triggered gravitational-wave burst search

We present the performance of searches for gravitational-wave bursts associated with external astrophysical triggers as a function of the search sky region. We discuss both the case of Gaussian noise and real noise of gravitational wave detectors for arbitrary detector networks. We demonstrate the ability to reach Gaussian limited sensitivity in real non-Gaussian data, and show the conditions required to attain it. We find that a single sky position search is � 20% more sensitive than an all-sky search of the same data.

Thermal Correction of Astigmatism in the Gravitational Wave Observatory GEO 600

The output port of GEOu2009600 is dominated by unwanted higher order modes (HOMs). The current thermal actuation system, a ring heater behind one of the folding mirrors, causes a significant amount of astigmatism, which produces HOMs. We have built and installed an astigmatism correction system, based on heating this folding mirror at the sides (laterally). With these side heaters and the ring heater behind the mirror, it is possible to tune its radius of curvature inxa0the horizontal and the vertical degree of freedom. We use this system to match the mirrors in the two arms of GEOu2009600 to each other, thereby reducing the contrast defect. The use of the side heaters reduces the power of the HOMs at thexa0output of GEOu2009600 by approximately 37%.

A fixed false alarm probability figure of merit for gravitational wave detectors

Performance of gravitational wave (GW) detectors can be characterized by several figures of merit (FOMs) which are used to guide the detectors commissioning and operations, and to gauge astrophysical sensitivity. One key FOM is the range in Mpc, averaged over orientation and sky location, at which a GW signal from binary neutron star inspiral and coalescence would have a signal-to-noise ratio (SNR) of 8 in a single detector. This fixed-SNR approach does not accurately reflect the effects of transient noise (glitches), which can severely limit the detectability of transient GW signals expected from a variety of astrophysical sources. We propose a FOM based instead on a fixed false-alarm probability (FAP). This is intended to give a more realistic estimate of the detectable GW transient range including the effect of glitches. Our approach applies equally to individual interferometers or a network of interferometers. We discuss the advantages of the fixed-FAP approach, present examples from a prototype implementation, and discuss the impact it has had on the recent commissioning of the GW detector GEO 600.

Upper-limit on the Advanced Virgo output mode cleaner cavity length noise

The Advanced Virgo detector uses two monolithic optical cavities at its output port to suppress higher order modes and radio frequency sidebands from the carrier light used for gravitational wave detection. These two cavities in series form the output mode cleaner. We present a measured upper limit on the length noise of these cavities that is consistent with the thermo-refractive noise prediction of 8× 10−16 m/Hz1/2 at 15Hz. The cavity length is controlled using Peltier cells and piezo-electric actuators to maintain resonance on the incoming light. A length lock precision of 3.5× 10−13 m is achieved. These two results are combined to demonstrate that the broadband length noise of the output mode cleaner in the 10-60Hz band is at least a factor 10 below other expected noise sources in the Advanced Virgo detector design configuration. PACS numbers: 04.80.Nn, 95.55.Ym ar X iv :1 70 3. 01 56 9v 2 [ ph ys ic s. in sde t] 1 1 Ju l 2 01 7 OMC length noise upper-limit 2