TITLE:   GCN CIRCULAR
NUMBER:  21974
SUBJECT: GRB 171004A: Swift/UVOT Upper Limits
DATE:    17/10/05 14:03:40 GMT
FROM:    Jeffrey Gropp at PSU  <jdg44@psu.edu>

J. D. Gropp (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 171004A
184 s after the BAT trigger (Cenko et al., GCN Circ. 21966).
No optical afterglow consistent with the refined XRT position
(Osborne et al. GCN Circ. 21970)
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 initial exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white              184         4143          233         >20.3
b                 3903         4103          197         >19.8
u                 3698         3898          197         >19.7


The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.02 in the direction of the burst
(Schlegel et al. 1998).