GCN Circular 29712

A. A. Breeveld (UCL-MSSL) and J. D. Gropp (PSU) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210323A 89 s after the BAT trigger 
(Gropp et al., GCN Circ. 29699
Not found
 
 
). The optical afterglow detected by Malesani et al. (GCN Circ. 29703
Not found
 
 
) 
and Pozanenko et al. (GCN Circ. 29708
Not found
 
 
) and consistent with the XRT position (Evans et al. GCN Circ. 
29704
Not found
 
 
), is not 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            89          239          147         >20.1
u_FC               302          552          246         >19.9
white               89         4948          569         >20.5
v                  632         1423           97         >17.7
b                  558         1522           97         >19.3
u                  302         1497          324         >19.3
w1                 681         1473           97         >18.5
m2                 828          848           19         >18.8
w2                 607         5034          136         >19.4

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of 
E(B-V) = 0.131 in the direction of the burst (Schlegel et al. 1998).