Igor Andreoni (Caltech) -- Deep Follow-Up of Gravitational Waves with DECam and GROWTH Facilities During O3

We are now half-way in the third observing run of the LIGO and Virgo gravitational wave detectors. Several gravitational wave events were discovered, including binary neutron star and neutron star -- black hole mergers. However, the search for an electromagnetic counterpart is more challenging than ever: the gravitational wave signals are detected at large distances (usually beyond 200 Mpc) and are coarsely localized. The GROWTH Collaboration is committed to searching for an electromagnetic counterpart using many telescopes, including the Zwicky Transient Facility (ZTF) and the Dark Energy Camera (DECam) wide-field optical imagers. The field of view of DECam is smaller than ZTF, but the depth of the observations is significantly larger, making the partnership between the two facilities a very productive discovery machine. I will present the GROWTH follow-up efforts since April 2019, focusing in particular on the results obtained with DECam observations.