  Gravitational waves searches for compact binary mergers with LIGO and Virgo
are presently a two stage process. First, a gravitational wave signal is
identified. Then, an exhaustive search over possible signal parameters is
performed. It is critical that the identification stage is efficient in order
to maximize the number of gravitational wave sources that are identified.
Initial identification of gravitational wave signals with LIGO and Virgo
happens in real-time which requires that less than one second of computational
time must be used for each one second of gravitational wave data collected. In
contrast, subsequent parameter estimation may require hundreds of hours of
computational time to analyze the same one second of gravitational wave data.
The real-time identification requirement necessitates efficient and often
approximate methods for signal analysis. We describe one piece of real-time
gravitational-wave identification: an efficient method for ascertaining a
signal's consistency between multiple gravitational wave detectors suitable for
real-time gravitational wave searches for compact binary mergers. This
technique was used in analyses of Advanced LIGO's second observing run and
Advanced Virgo's first observing run.
