Detector characterisation and searches for gravitational waves using GEO 600

• Main Author: Adams, Thomas
• Published: Cardiff University 2014
• Subjects: 523.01; QB Astronomy
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611043

We are currently on the brink of the first direct detection of gravitational waves (GWs) with a new generation of GW detectors currently being commissioned. In the period before the advanced detectors come online we must prepare techniques for detector characterisation and advanced data analysis methods to improve our sensitivity to potential sources of GWs. We begin with an outline of GWtheory, derived from Einstein’s general theory of relativity. We introduce each of the main classes of GWsignals, as distinguished by the GW community, focusing mainly on GW bursts. A short outline is also given for compact binary coalescences, continuous waves, and stochastic background. An introduction to GW interferometers is then given, focusing mainly on the GEO600 detector. The stationary noise sources that limit the frequency dependent sensitivity of current GW detectors are discussed: optical readout noise, thermal noise, and seismic noise. We discuss transient noise events (glitches) and the veto methods that are used to remove these events from the GW data channel. Details are given for glitch hunting that was performed at GEO 600 to identify and understand sources of transient noise. We demonstrate a cost-benefit analysis method that could be used for increasing the number of observable sources, by assessing the severity of detector noise sources to efficiently guide commissioning. We introduce X-PI P E L I N E, a coherent search pipeline for GW bursts associated with astrophysical transients such as gamma-ray bursts, and give details of pipeline line development that we were involved in. Results from a search for GW associated with 78 gamma-ray bursts that occurred while only GEO 600 and one of the LIGO or Virgo detectors were taking data are presented; these events have not previously been analysed. The sensitivity of searches for GW bursts is often critically limited by non-Gaussian noise fluctuations that are difficult to distinguish from real signals. We utilised the boosted decision tree multivariate analysis classifier to probe the full space of measured properties of events in an attempt to maximise the power to accurately classify events as signal or background, compared to the standard X-PI P E L I N E. While the LIGO and Virgo detectors are undergoing intense commissioning, GEO600 is the only GW detector taking observations. Therefore, we demonstrate the feasibility of performing a single detector analysis for GW bursts using GEO 600 in preparation for any exceptional astrophysical events (such as a Galactic supernova).