TITLE:   GCN CIRCULAR
NUMBER:  29615
SUBJECT: GRB 210305A: Swift/UVOT Upper Limits
DATE:    21/03/07 19:43:36 GMT
FROM:    Alexander Belles at PSU/Swift  <aub1461@psu.edu>

A. Belles (PSU) and A. D'Ai (INAF-IASFPA)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210305A
85 s after the BAT trigger (D'Ai et al., GCN Circ. 29595).
No optical afterglow consistent with the XRT position
(D'Ai et al. GCN Circ. 29595)
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            86          235          147         >20.19
u_FC               298          548          245         >19.54
white              577         1721          264         >20.51
v                  627         1771          134         >18.55
b                  553         1696          116         >19.37
u                  700         1672           97         >18.86
w1                 676         1818          134         >18.70
m2                 651         1795          136         >18.63
w2                 603         1746          136         >18.60

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.155 in the direction of the burst
(Schlegel et al. 1998).