Session S14: Advances in Ground-based Gravitational Wave Detection

Improving the performance of the Enhanced LIGO detectors

Since July 2009, enhanced Laser Interferometer Gravitational-Wave Observatory (LIGO) interferometers in Livingston, LA, and Hanford, WA have been collecting science data at record sensitivities. The detectors underwent a nearly two year long upgrade which changed the gravitational wave readout scheme and increased the laser power in order to achieve this improved performance. Although the new science run has begun, commissioning of the interferometers continues. Some of the latest developments in the hardware and control of the detectors and specific efforts to reach their design sensitivity goal will be discussed.   

Evanescent-wave heat transfer between two parallel plates of sapphire

Evanescent-wave heat transfer is the process in which near-field radiation effects are used to transfer heat from one body to another. These evanescent waves allow a thermal transmission through a small gap that is several orders of magnitude greater then the thermal transmission of far-field blackbody radiation. Although heat transfer using evanescent waves was first theatrically explained in the early 1970's by Polder and Van Hove, experimental testing of this theory remains sparse. We will describe experiments to measure the heat transfer between two parallel plates due to evanescent waves. Ultimately, this method of heat transfer may be used to cool the test masses in future upgrades of the Laser Interferometer Gravitational-wave Observatories.   

Estimating the Rate of False Signals in LIGO's Compact Binary Coalescence Gravitational-wave Searches

The method of time-shifted data has traditionally been the technique used to estimate the rate of false signals in LIGO's non-stationary, non-Gaussian instrumental noise. However, this method fails to provide a rate for any gravitational-wave candidates with a higher ranking-statistic than the highest-ranked false signal in any of the time-shifted data. I will discuss new methods of estimating the rate of false signals via single detector instrumental noise and new techniques involving time-shifted data. I will demonstrate how each of these new methods will improve our ability to attach false signal rates to our gravitational-wave candidates.   

Separating Gravitational Wave Signals from Instrument Artifacts

Central to the gravitational wave detection problem is the challenge of distinguishing features in the data caused by the instrument from those caused by astrophysical sources. This capability has been demonstrated for Gaussian noise, however, transient noise excursions, or ``glitches,'' remain problematic. While detector diagnostics and coincidence tests can reject most glitches which may be considered gravitational wave events, a procedure that robustly differentiates the two is desirable. We have developed an approach for coherently fitting to noise excursions without degrading the underlying gravitational wave signal. The principal feature is the use of wavelets as ``glitch templates'' to match the non-Gaussian components of the noise, the number of which is determined by a trans-dimensional Markov chain Monte Carlo. We demonstrate the method's effectiveness on simulated data containing low amplitude gravitational wave signals from in-spiraling binary black hole systems, Gaussian noise in accordance with the LIGO/Virgo network of detectors, and injected glitches of various amplitude, prevalence, and variety.   

Directional searches for persistent gravitational waves

A stochastic gravitational-wave background can arise from a wide variety of processes including inflation, cosmic strings, phase transitions in the early universe, pre-Big- Bang models and the superposition of astrophysical sources such as gamma-ray bursts. In addition to this background, the gravitational-wave sky may include a significant foreground from nearby point-like sources. In general, the angular distribution of gravitational-wave power is not strongly constrained. We thus propose a novel framework for directional analysis of persistent (non-bursting) and unmodeled gravitational waves with a network of interferometers, which allows for arbitrary angular distributions of gravitational-wave power.   

Extending the Reach of Gravitational Wave Astronomy: Detection without Characterization

Gravitational waves (GW) that may be too weak to be characterized or quantified may still be strong enough to be detected using statistical approaches. Similar to observing the light from a stellar cluster without resolving the individual stars, we seek to answer the question of whether GW signals may be detected to greater distances without providing a quantification of the wave. We describe a Bayesian approach to the problem of weak GW detection in noisy data. We identify the contribution of the observations to the odds that a signal is present. We demonstrate this method by examining a range of simulated signals and computing the volume of space over which a confident detection may be made. Finally, we compare the volume estimate to present detection methods, which utilize a signal to noise ratio threshold to characterize detections.   

An all-sky search for continuous gravitational waves from neutron stars in binary systems using the TwoSpect algorithm

A search for continuous gravitational waves (GWs) from unknown pulsars in binary systems is notorious for its computational challenge. Data analysis techniques for GWs from unknown isolated sources have been in use for a number of years, while all-sky analysis techniques for sources in binaries have only recently begun development. We present a hierarchical binary search method called TwoSpect, which exploits the periodic orbital modulations of the source waves by searching for patterns in doubly-Fourier-transformed data. We will describe recent developments of the TwoSpect search pipeline, including its mitigation of detector noise variations and corrections for Doppler frequency modulation caused by changing detector velocity. Sensitivity estimates based on simulations will be presented.   

The Observational Limits of Ground Based Gravitational Wave Detectors: Core-collapse Supernovae

Because they emerge unimpeded, the gravitational wave signatures of core-collapse SNe carry information about the progenitor and proto-neutron star or black hole that is otherwise beyond our observational reach. The wealth of astrophysical data, such as mass, rotation rate, degree of differential rotation, and bounce depth, that can be recovered from gravitational radiation produced by core-collapse SNe, presents an opportunity to gain significant insight into the physical processes underlying these events. We evaluate the sensitivity of current and future networks of ground-based GW detectors to GWs from stellar core-collapse SNe at varying distances from the Earth and place limits on their detectability.