LIGO interferometer operating at design sensitivity with application to gravitational radiometry

Abstract

During the last decade the three interferometers of the Laser Interferometer Gravitational Wave Observatory (LIGO) were built and commissioned. In fall 2005 design sensitivity was achieved, corresponding to a strain sensitivity of 2.5 x 10-23 Hz-1/2 at 150 Hz. All three interferometers are now in an extended science run. One of the most critical steps to reach this goal was increasing the power in the interferometer to more than 200 Watt at the beam splitter. This required the commissioning of both a thermal compensation system and shot noise limited sensing electronics capable of detecting all the light. Additionally, a series of unexpected noise sources had to be mitigated. This work is described in the first part of this thesis. In a second part I introduce a radiometer analysis that is capable of spatially resolving anisotropies in a stochastic gravitational wave background. The analysis is optimized for identifying point sources of stochastic gravitational radiation. Finally, data from the fourth LIGO science run is used to set both isotropic and directional upper limits on the stochastic background of gravitational waves.

(cont.) The bound set on the normalized gravitational wave energy density is h2 gw(f) < 6.25 x 10-5 and the limit set on a broadband and flat strain power spectrum coming from a point source varies between 8.5 x 10-49Hz-1 and 6.1 x 10-48Hz-1, depending on the source position. Additionally a limit on gravitational radiation coming from the direction of Sco-X1, the brightest X-ray source short of the sun, is set for each frequency bin.