  In this paper, we estimate the eccentricity of the 10 BBHs in GWTC-1 by using
the inspiral-only BBH waveform template EccentricFD. Firstly, we test our
method with simulated eccentric BBHs. Afterwards we apply the method to the
real BBH gravitational wave data. We find that the BBHs in GWTC-1 except
GW151226, GW170608 and GW170729 admit very small eccentricity. Their upper
limits on eccentricity range from 0.033 to 0.084 with 90% credible interval at
the reference frequency 10 Hz. For GW151226, GW170608 and GW170729, the upper
limits are higher than 0.1. The relatively large eccentricity of GW151226 and
GW170729 is probably due to ignoring the effective spin and low signal-to-noise
ratio, and GW170608 is worthy of follow-up research. We also point out the
limitations of the inspiral-only non-spinning waveform template in eccentricity
measurement. The measurement of BBH eccentricity helps to understand its
formation mechanism. With the increase in the number of BBH gravitational wave
events and the more complete eccentric BBH waveform template, this will become
a viable method in the near future.
