GCN Circular 30425

M. H. Siegel (PSU) and B. Sbarufatti (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210708A
121 s after the BAT trigger (Sbarufatti et al., GCN Circ. 30413
Not found
 
 
).
No optical afterglow consistent with the XRT position
(Sbarufatti et al. GCN Circ. 30413
Not found
 
 
) is detected in the initial UVOT exposures.
We note that the XRT position is close to the bright star HD 100708,
the brightness of which may obscure a faint afterglow.
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

u_FC               121          370          246         >19.4
v                  427         4406          236         >19.6
b                  377         5077          108         >19.3
u                  121         5021          481         >19.4
w1                 476         4816          236         >18.9
m2                 452         4611          236         >19.4
w2                 403         4201          236         >19.5

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.160 in the direction of the burst
(Schlegel et al. 1998).