  To determine the polarization character of gravitational waves, we use strain
data from the GW170814 binary black hole coalescence event detected by the
three LIGO-Virgo observatories, extracting the gravitational wave strain signal
amplitude ratios directly from those data. Employing a geometric approach that
links those ratios to the gravitational wave polarization properties, we find
that there is a range of source sky locations, partially overlapping the
LIGI-Virgo 90% credible range of GW170814 source locations, for which vector
polarization is consistent with the observed amplitude ratios. A Bayesian
inference analysis indicates that the GW170814 data cannot rule out vector
polarization for gravitational waves. Confirmation of a vector polarization
component of gravitational waves would be a sign of post-general relativity
physics.
