TITLE:   GCN CIRCULAR
NUMBER:  31277
SUBJECT: GRB 211221A: MeerLICHT optical limits
DATE:    21/12/22 10:54:04 GMT
FROM:    Simon de Wet at UCT  <dwtsim002@myuct.ac.za>

P.J. Groot (Radboud/UCT/SAAO), S. de Wet (UCT), D. B. Malesani
(Radboud/DAWN,NBI),
P.M. Vreeswijk (Radboud), report on behalf of the MeerLICHT consortium:

The position of GRB211221A (Page et al., GCN 31273; Evans et al., GCN
31275; Lipunov et al., GCN 31274; Malesani et al., GCN 31276) was
observed with the 0.6m wide-field MeerLICHT telescope, located at
Sutherland, South Africa, starting at 2021-12-22, 00:24 UT,
approximately 3.5 hr after the detection by Swift. A series of 60s
observations in the u,g,q,r,i,z bands was started that lasted until
2021-12-22, 01:21 UT. All data was processed automatically using the
BlackBOX/ZOGY pipeline (Vreeswijk et al, forthcoming). Cloudy
conditions prevented observations earlier in the night.

Co-adding the single exposures in each filter leads to deeper 3-sigma
AB-magnitude limits at the Swift-XRT position reported by
Evans et al. (GCN 31275) of:

u > 19.97 at 00:51:03 UT
g > 20.55 at 01:02:18 UT
q > 21.85 at 00:59:14 UT
r > 20.67 at 00:56:55 UT
i > 20.32 at 00:52:09 UT
z > 19.70 at 00:56:24 UT.

These limits are consistent with those reported by Malesani et
al. (GCN 31276) taken at the same time.

MeerLICHT is built and run by a consortium consisting of Radboud
University, University of Cape Town, the South African Astronomical
Observatory, the University of Oxford, the University of Manchester
and the University of Amsterdam