L. Matone

Search method for unmodeled transient gravitational waves associated with SGR flares

We describe a method for searching for transient gravitational waves associated with soft gamma-ray repeater (SGR) flares or other burst-like events using data collected by interferometric gravitational wave detectors. The method can be used to analyze data from either a single detector or from two detectors coherently. The excess power-type algorithm creates event sets from conditioned detector data which may be compared to signal simulations of known strength based on plausible waveform classes. Estimated search sensitivities obtained by performing two-detector searches on the simulated data are presented. In the case of 22 ms duration white noise bursts in the 100–200 Hz band injected into simulated noise, we find a characteristic strain sensitivity h90%rss = 3.0 × 10−22 .

Accurate measurement of the time delay in the response of the LIGO gravitational wave detectors

We present a method to precisely calibrate the time delay in a long baseline gravitational-wave interferometer. An accurate time stamp is crucial for data analysis of gravitational wave detectors, especially when performing coincidence and correlation analyses between multiple detectors. Our method uses an intensity-modulated radiation pressure force to actuate on the mirrors. The time delay is measured by comparing the phase of the signal at the actuation point with the phase of the recorded signal within the calibrated data stream used for gravitational wave searches. Because the signal-injection path is independent of the interferometers control system, which is used for the standard calibration, this method can be an independent verification of the timing error in the system. A measurement performed with the 4 km interferometer at the LIGO Hanford Observatory shows a 1 µs relative accuracy when averaging over 50 min. Our understanding of the systematic time delay in the detector response has reached the level of 10 µs.

Search algorithm for the detection of long-duration narrow-band transients in GW interferometers

The recent observation of quasi-periodic oscillations (QPOs) in the x-ray light curve of soft gamma-ray repeaters, which fall within LIGOs sensitivity band, prompted us to search for gravitational waves associated with them. We describe the corresponding search algorithm that is based on the energy measurement in a single detector signal stream. We analytically derive the search sensitivity and compare it to the numerical sensitivity provided by the analysis pipeline with simulated detector noise. We found excellent agreement between the two approaches, reassuring us that the analysis method is well understood and implemented properly. The detector noise is approximated as white Gaussian with a strain equivalent spectral noise density of 10−22 strain Hz−1/2, similar to the noise floor of the H1 LIGO detector at the time of the SGR 1806–20 hyperflare event of 27 December 2004. As a trial model, we use a hypothetical 100 Hz QPO lasting for 50s. The corresponding energy sensitivity is found to be Esens = 3.63 × 10−43 strain2 Hz−1 which, in terms of amplitude, is hsensrss-det = 6.06 × 10−22 strain Hz−1/2. We show that, besides being simple and flexible, the algorithm is sensitive to a wide range of waveforms obeying the time and bandwidth requirements.

Searching for Cataclysmic Cosmic Events with a Coincident Gamma‐ray Burst and Gravitational Wave Signature

Coincident observation of gamma‐ray bursts and gravitational waves will help us to dramatically improve our understanding of energetic processes in the universe while opening a new window on compact, and often difficult to study, astronomical objects. One of the major goals of interferometric gravitational wave detectors is to develop and exploit gravitational wave detection in conjunction with astrophysical observations. The collaboration among gravitational wave detectors and gamma‐ray burst observatories is ongoing and flourishing. The present status of the collaborative research and the future plans are summarized and illustrated through practical experience with the Laser Interferometer Gravitational Wave Observatory (LIGO) detectors.

Detecting long-duration narrow-band gravitational wave transients associated with soft gamma repeater quasiperiodic oscillations

We have performed an in-depth concept study of a gravitational wave data analysis method which targets repeated long quasi-monochromatic transients (triggers) from cosmic sources. The algorithm concept can be applied to multi-trigger data sets in which the detector-source orientation and the statistical properties of the data stream change with time, and does not require the assumption that the data is Gaussian. Reconstructing or limiting the energetics of potential gravitational wave emissions associated with quasi-periodic oscillations (QPOs) observed in the X-ray lightcurve tails of soft gamma repeater flares might be an interesting endeavour of the future. Therefore we chose this in a simplified form to illustrate the flow, capabilities, and performance of the method. We investigate performance aspects of a multi-trigger based data analysis approach by using O(100 s) long stretches of mock data in coincidence with the times of observed QPOs, and by using the known sky location of the source. We analytically derive the PDF of the background distribution and compare to the results obtained by applying the concept to simulated Gaussian noise, as well as off-source playground data collected by the 4-km Hanford detector (H1) during LIGOs fifth science run (S5). We show that the transient glitch rejection and adaptive differential energy comparison methods we apply succeed in rejecting outliers in the S5 background data. Finally, we discuss how to extend the method to a network containing multiple detectors, and as an example, tune the method to maximize sensitivity to SGR 1806-20 flare times.

Benefits of artificially generated gravity gradients for interferometric gravitational-wave detectors

We present an approach to experimentally evaluate gravity gradient noise, a potentially limiting noise source in advanced interferometric gravitational-wave detectors. In addition, the method can be used to provide sub-percent calibration in phase and amplitude. Knowledge of calibration to such certainties shall enhance the scientific output of the instruments in the case of an eventual detection of gravitational waves. The method relies on a rotating symmetrical two-body mass, a dynamic gravity field generator (DFG). The placement of the DFG in the proximity of one of the interferometers suspended test masses generates a change in the local gravitational field detectable with current interferometric gravitational-wave detectors.

Prospects of gravitational wave data mining and exploration via evolutionary computing

Techniques of evolutionary computing have proven useful for a diverse array of fields in science and engineering. Because of the expected low signal to noise ratio of LIGO data and incomplete knowledge of gravitational waveforms, evolutionary computing is an excellent candidate for LIGO data analysis studies. Using the evolutionary computing methods of genetic algorithms and genetic programming, we have developed, as a proof of principle, search algorithms that are effective at finding sine-gaussian signals hidden in noise while maintaining a small false alarm rate. Because we used realistic LIGO noise as a training ground, the algorithms we have evolved should be well suited to detecting signals in actual LIGO data, as well as in simulated noise. These algorithms have continuously improved during the five days of their evolution and are expected to improve further the more they are evolved. The top performing algorithms from generation 100 and 199 were benchmarked using gaussian white noise to illustrate their performance and the improvement over 100 generations.