Searching binary compact objects in earth-based detectors

In 1998, I solved (with Sanjeev Dhurandhar and Archana Pai) the problem of obtaining the optimal statistic for searching inspiral signals from binary compact objects in multiple detectors. Since these signals are very well modeled, a binary inspiral event may well be the first gravitational wave event to be detected. Their search in multiple detectors (to mitigate false-alarms) constitutes a critical pursuit in gravitational wave astronomy today. In the above work, we also showed how the analytic maximization over the gravitational wave polarization angle, $\psi$, and the orbit's inclination angle, $\iota$, can be effected [Bose:1999bp, Bose:1999pj], thus reducing the computational costs enough to make such coherent searches in a limited number of detectors viable [Pai:2001cf]. A detailed study of the implementation of this network search (known variously as coherent search, aperture synthesis, and interferometry with interferometers), the signal-parameter space metric, estimates of the number of templates, etc., is given in Ref. [Pai:2001cf]. The results and methods of the above papers have already been used in the first string of observational papers [LIGO Papers]. Many aspects of our work have applications beyond inspiral signals and have motivated the formulation of coherent detection statistics also for unmodeled / burst signals (see, e.g., Refs. [Finn:2000hj,Arnaud:2003zr,Arnaud:2003zq,Vicere:2001ye,Sylvestre:2003gm,Sylvestre:2003vc] ), detection of galactic binaries with LISA [Pai:2001cf,Rogan:2004wq], and detection with other detectors (such as spherical detectors [Magalhaes:2005jj,Lobo:2001ea]).

The code for performing a coherent search in data from up to 4 detectors has been developed by me and my students, Shawn Seader and Jeff Noel, with a lot of input from several members of the LIGO Scientific Collaboration (LSC). (Those who have experience in code development for multi-parameter, multi-detector searches for low SNR signals will know how challenging and time-consuming such work is, while not being the most visible part of an observational paper.) These 4 detectors could be, e.g., the 3 LIGO detectors as well as a fourth detector, chosen from GEO, VIRGO or TAMA. The code is flexible enough to be easily extended to include more detectors. Also, the code does not even require the gravitational wave strain data to work; all it needs are, what we call, "C" time-series data, which are analogous to the SNR time-series. We foresee that the participating detector communities will be more forthcoming in exchanging such meta-data time-series. This code has been tested on LIGO data and is now being readied to search on data from LIGO, GEO, and (mock-data) from Virgo. Such applications and the ensuing results make the effort very rewarding. (The prototyping and testing of this code was done on our supercomputing cluster, Pleiades.