GWTC-3 is the third Gravitational-Wave Transient Catalog from LIGO, Virgo, and KAGRA. GWTC-3 updates our previous catalogs with gravitational-wave observations from the second part of Observing Run 3 (imaginatively called O3b), which lasted from November 2019 to March 2020. Collectively, GWTC-3 represents the largest number of gravitational-wave observations assembled to date. So, what gravitational-wave catalogs have there been so far?
- GWTC-1, which contains a total of 11 events from the first and second observing runs (O1 and O2).
- GWTC-2, which added 39 events to GWTC-1, bringing the total number of events to 50 (from O1, O2, and O3a, the first part of O3).
- GWTC-2.1 revisited the O3a analysis, finding an additional 8 candidates, but also reclassifying 3 of the original GWTC-2 candidates because their probability of being real astrophysical signals dropped to less than 50% (see the “Detecting gravitational waves” section below). This brought the total to 55 events.
- GWTC-3 (this paper) adds a further 35 gravitational-wave events from O3b, bringing the total number of events observed to date to a whopping 90. (Figure 3 below illustrates the sheer number and our growing population of detected events).
In O3b, KAGRA joined LIGO and Virgo for the final part of the run and in April 2020 completed a two-week observation run with the GEO 600 detector located in Germany. The results of this observing run will be presented separately.