TITLE:   GCN CIRCULAR
NUMBER:  21388
SUBJECT: GRB 170728B: Swift/UVOT Upper Limits
DATE:    17/07/30 01:46:56 GMT
FROM:    Sam LaPorte at PSU  <sjl5346@psu.edu>

GRB 170728B: Swift/UVOT Upper Limits

S. J. Laporte (PSU) and S. B. Cenko (GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170728B
473 s after the BAT trigger (Cenko et al., GCN Circ. 21371).
No optical afterglow consistent with the optical position
(D'Avanzo et al. GCN Circ. 21373)
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           473          623          147         >19.8
white              473         7867          908         >20.8
v                  630         8278          627         >19.6
b                  728        14417         1117         >21.3
u                  703        13868         1276         >21.2
w1                 679        19251         2000         >21.6
m2                6847        18681         1279         >22.1
w2                6437         8073          393         >21.5

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.03 in the direction of the burst
(Schlegel et al. 1998).