TITLE:   GCN CIRCULAR
NUMBER:  28851
SUBJECT: GRB 201104B: Swift/UVOT Detection
DATE:    20/11/06 09:41:59 GMT
FROM:    Samantha Oates at MSSL  <samantha.oates@alumni.ucl.ac.uk>

S. R. Oates (U.Birmingham) and B. Sbarufatti (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 201104B
56 s after the BAT trigger (Sbarufatti et al., GCN Circ. 28825).
A source consistent with the XRT position (Sbarufatti et al. GCN Circ. 28825)
and UVOT position (Marshall et al. GCN Circ. 28827) is detected in the initial UVOT exposures.

Preliminary detections and 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: 

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag
white  (FC)         56          206          147         17.98 +/- 0.05
white            20890        21385          484        >21.1
b                 3718         3777           57        >19.0
u (FC)             268          459          188         18.72 +/- 0.16

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.048 in the direction of the burst
(Schlegel et al. 1998).