  We propose a blind, template-free method for the extraction of a common
signal between the Hanford and Livingston detectors and apply it especially to
the GW150914 event. We construct a log-likelihood method that maximizes the
cross-correlation between each detector and the common signal and minimizes the
cross-correlation between the residuals. The reliability of this method is
tested using simulations with an injected common signal. Finally, our method is
used to assess the quality of theoretical gravitational wave templates for
GW150914.
