  We report the detection of new binary black hole merger events in the
publicly available data from the second observing run of advanced LIGO and
advanced Virgo (O2). The mergers were discovered using the new search pipeline
described in Venumadhav et al. [Phys. Rev. D 100, 023011 (2019)], and are above
the detection thresholds as defined in Abbott et al. (LIGO Scientific and Virgo
Collaborations) [Phys. Rev. X 9, 031040 (2019).] Three of the mergers
(GW170121, GW170304, GW170727) have inferred probabilities of being of
astrophysical origin $p_{\rm astro} > 0.98$. The remaining three (GW170425,
GW170202, GW170403) are less certain, with $p_{\rm astro}$ ranging from 0.5 to
0.8. The newly found mergers largely share the statistical properties of
previously reported events, with the exception of GW170403, the least secure
event, which has a highly negative effective spin parameter $\chi_{\rm eff}$ .
The most secure new event, GW170121 ($p_{\rm astro} > 0.99$), is also notable
due to its inferred negative value of $\chi_{\rm eff}$, which is inconsistent
with being positive at the ~95.8% confidence level. The new mergers nearly
double the sample of gravitational wave events reported from O2, and present a
substantial opportunity to explore the statistics of the binary black hole
population in the Universe. The number of detected events is not surprising
since we estimate that the detection volume of our pipeline may be larger than
that of other pipelines by as much as a factor of two (with significant
uncertainties in the estimate). The increase in volume is larger when the
constituent detectors of the network have very different sensitivities, as is
likely to be the case in current and future runs.
