TITLE: GCN CIRCULAR NUMBER: 29141 SUBJECT: GRB 201221D: LCOGT upper limits DATE: 20/12/22 19:18:16 GMT FROM: Igor Andreoni at Caltech Igor Andreoni (Caltech), Michael M. Coughlin (UMN) on behalf of the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration We used the Sinistro camera on the 1-m LCO Global Telescope Network (LCOGT, Brown et al., 2013) to observe the afterglow of short-duration GRB 201221D (Page et al., GCN #29112). Two sets of 300s exposures were acquired in g-r-i bands between 2020-12-22T07:57 and 2020-12-22T08:47 UTC. The observations were performed under proposal IDs TOM2020A-008 (PI Andreoni) and NOAO2020B-005 (PI Coughlin). We do not identify any source within 3.9 arcsec of the enhanced Swift-XRT position (Evans et al., GCN #29119). Photometric upper limits, calibrated against Pan-STARRS DR1 magnitudes (Chambers et al., 2016), were measured to be g > 22.8, r > 22.2, and i > 21.5 mag (5-sigma) after image stacking. The candidate optical counterpart (transient or host galaxy: Malesani et al., GCN #29117; Dichiara et al., GCN #29128; de Ugarte Postigo et al., GCN #29132; Kilpatrick et al., GCN #29133) is too faint to be detectable in our observations, which did not show any significant brightening, as expected. We thank the TOM Community Development Program and the TOM Toolkit Workshop organizers for the generous LCOGT time allocation. GROWTH is a worldwide collaboration comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan; IIT-B, India; IIA, India; LJMU, TTU, USyd, Australia, and SDSU, USA. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949.