TITLE:   GCN CIRCULAR
NUMBER:  30425
SUBJECT: GRB 210708A: Swift/UVOT Upper Limits
DATE:    21/07/08 20:24:24 GMT
FROM:    Mike Siegel at PSU/Swift MOC  <mhs18@psu.edu>

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).
No optical afterglow consistent with the XRT position
(Sbarufatti et al. GCN Circ. 30413) 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).