GWTC-2.1: Deep extended catalog of compact binary coalescences observed by LIGO and Virgo during the first half of the third observing run

GWTC-2.1 is a catalog of gravitational wave events from compact binary coalescences from the first half of the third observing run of Advanced LIGO and Advanced Virgo. It improves on GWTC-2, which covered the same period but with less refined analysis methods. GWTC-2.1 identifies 8 new events, all identified as sourced by binary black holes with one exception identified as a neutron star-black hole coalescence. These events expand significantly on the parameters characterizing the sources of observed gravitational-wave transients.