Search techniques for gravitational waves from black-hole ringdowns

Of all the astronomical sources of gravitational radiation, the ringdown waveform arising from a small perturbation of a spinning black hole is perhaps the best understood: for the late stages of such a perturbation, the waveform is simply an exponentially damped sinusoid. Searching interferometric gravitational wave antenna data for these should be relatively easy. In this paper, I present the results of a single-filter search for ringdown waveforms arising from a 50 solar mass black hole with $98\%$ of its maximum spin angular momentum using data from the Caltech 40-m prototype interferometer. This search illustrates the techniques that may be used in analyzing data from future kilometer-scale interferometers and describes some of the difficulties present in the analysis of interferometer data. Most importantly, it illustrates the use of coincident events in the output of two independent interferometers (here simulated by 40-m data at two different times) to substantially reduce the spurious event rate. Such coincidences will be essential tools in future gravitational wave searches in kilometer-scale interferometers.