TITLE:   GCN CIRCULAR
NUMBER:  29129
SUBJECT: GRB 201221D: Swift/UVOT Upper Limits
DATE:    20/12/22 13:27:07 GMT
FROM:    Alice Breeveld at MSSL-UCL  <a.breeveld@ucl.ac.uk>

A. A. Breeveld (UCL-MSSL) and K. L. Page (U. Leicester) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 201221D 92 s after the BAT trigger 
(Page et al., GCN Circ. 29112). No optical afterglow consistent with the NOT or XRT position 
(Malesani et al. GCN Circ. 29117; Evans et al. GCN Circ. 29119) is detected in the initial UVOT 
exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. 
Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC            92          242          147         >20.3
u_FC               305          554          246         >19.3
white             4047         4247          197         >21.0
v                  634         4657          216         >19.2
u                  305         5110          282         >19.4
w1                 684         5068          216         >19.7
m2                4663         4863          197         >19.5
w2                4253         4453          197         >19.9

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of 
E(B-V) = 0.02 in the direction of the burst (Schlegel et al. 1998).