Gravitational Wave Candidate Identification in GWTC-3

GWTC-3 is the latest version of the LIGO, Virgo, Kagra Collaboration's Gravitational Wave Transient Catalog, comprising compact binary coalescence gravitational wave candidates from the first three observing runs. This latest iteration of the catalog adds 35 candidate gravitational waves from the second part of the third observing run (O3b), bringing the cumulative total to 90 candidates. There are 17 new candidates which were not previously reported as low-latency alerts during O3b. All of the candidates added to the catalog are consistent with either binary black hole coalescences or neutron-star black hole coalescences. Each of these events pass a threshold on the probability of astrophysical origin, p(astro) > 0.50. We additionally publish a list of 7 marginal candidates which fail to meet the p(astro) threshold but pass a false alarm rate (FAR) threshold 2 per year. A bulk data release further includes a deep subthreshold list of triggers which fail to meet the previous two thresholds but have FAR 2 per day. These candidates come from an offline re-analysis of the O3b detector data by four independent search pipelines: cWB, GstLAL, MBTA and PyCBC. We discuss the search methods used in this work as well as an overview of the candidate events found.