GCN Circular 29141

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.