Gravitational Wave Studies: Detector Calibration and an All-Sky Search for Spinning Neutron Stars in Binary Systems.

Abstract

The Laser Interferometer Gravitational wave Observatory (LIGO) Project has constructed three, kilometer-scale gravitational wave detectors in the United States. These detectors have achieved unprecedented levels of differential-length sensitivity in a quest to directly observe the spacetime oscillations produced by gravitational waves from astrophysical sources. These waves can provide new observations and insight into some of the most energetic, exotic, and violent events in the Universe.

Strain calibration of gravitational wave detectors is crucial for waveform reconstruction and source localization. Scientific reach is substantially improved if the calibration uncertainty can be reduced to the level of 1%. Toward this end, we have developed two fundamentally different precision test mass actuator calibration techniques to compare with the traditional calibration method, which measures a critical component of the key interferometer servo control loop that determines the gravitational wave output signal. We have compared our results from the three techniques in order to investigate systematic uncertainties associated with each technique.

A potential class of gravitational wave sources are rapidly spinning neutron stars with non-axisymmetric mass distributions, which generate quasi-monochromatic continuous gravitational waves. While search methods for unknown isolated spinning stars are approaching maturity, there have been no previous searches for unknown spinning stars in binary systems. Current search methods for isolated stars are already computationally limited; expanding the parameter space searched to include binary systems is a formidable challenge. We present a new hierarchical binary search method called TwoSpect, which exploits the periodic orbital modulations of the continuous waves by searching for patterns in doubly Fourier-transformed data. We will describe the TwoSpect search pipeline, including its mitigation of detector noise variations and corrections for Doppler frequency modulation caused by changing detector velocity. Tests on simulated data and on a sample of detector data will be presented.