TITLE:   GCN CIRCULAR
NUMBER:  29712
SUBJECT: GRB 210323A: Swift/UVOT Upper Limits
DATE:    21/03/24 15:26:43 GMT
FROM:    Alice Breeveld at MSSL-UCL  <a.breeveld@ucl.ac.uk>

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). The optical afterglow detected by Malesani et al. (GCN Circ. 29703) 
and Pozanenko et al. (GCN Circ. 29708) and consistent with the XRT position (Evans et al. GCN Circ. 
29704), 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).