Overview of LIGO Scientific Collaboration inspiral searches

We describe the effort of inspiral searches with LIGO data from the third and fourth science runs, which took place in 2003/2004 and 2005, respectively. Although the analysis pipeline is the same for all searches, there are significant differences between the three major ongoing searches: for primordial black hole binaries, binary neutron stars and binary black holes. The horizon distance for all searches significantly increased with respect to earlier LIGO science searches. PACS numbers: 04.80.Nn, 95.85.Sz The search for gravitational waves has entered a new era with the operation of kilometre-scale laser interferometers. These L-shaped instruments are sensitive to the minute changes in the relative lengths of their orthogonal arms that would be produced by gravitational waves [1]. The Laser Interferometer Gravitational-Wave Observatory (LIGO) [2, 3] consists of three Fabry–Perot–Michelson interferometers: two interferometers are housed at the LIGO Hanford Observatory, Washington and a single interferometer is housed in the LIGO Livingston Observatory, Louisiana. In 2003–2005, all three interferometers simultaneously collected data under stable operating conditions during two science runs: the third science run from 31 October 2003 to 9 January 2004 (S3) and the fourth science run from 22 February 2005 to 24 March 2005 (S4). Even though the interferometers were not yet performing at their design sensitivity, the data represented the best broadband sensitivity to gravitational waves that had been achieved to that date [4, 5]. In this paper, an overview is given on the searches for signals from binary systems of compact stars, in the late inspiral stage of their evolution before coalescence. The searches include data from the third and fourth science runs of LIGO, including data from the GEO600 detector [6], which is located near Hannover, Germany. The first stage of an inspiral search consists of the creation of a bank of templates, which are used for matched filtering (a cross-correlation function between the data and the assumed waveform of the signal, see [7, 9]). Those templates, spanning the region in parameter space that is searched, defined by the binary component masses, are created in such a way that the loss in SNR between any putative signal and its nearest template is no more than a few per 0264-9381/06/190705+03$30.00 © 2006 IOP Publishing Ltd Printed in the UK S705 LIGO-P060081-00-Z