GCN Circular 19984

A. A. Breeveld (UCL-MSSL) and P. A. Evans (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 161004A
85 s after the BAT trigger (Evans et al., GCN Circ. 19979
Not found
 
 
).
A source consistent with the enhanced XRT position (Beardmore et al., 
GCN Circ. 19983
Not found
 
 
) is detected in the initial UVOT exposures in the white 
and u filters only.

The preliminary UVOT position is:
     RA  (J2000) =  17:32:36.54 = 263.15224 (deg.)
     Dec (J2000) = -00:57:02.7  =  -0.95075 (deg.)
with an estimated uncertainty of 0.56 arc sec. (radius, 90% confidence).

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               85          235          147         19.47 �� 0.16
v                  627         6121          432        >20.1
b                  552        10926         1144        >21.8
u                  297          547          246         19.55 �� 0.29
w1                 848         6531          413        >20.2
m2                4690         6326          393        >20.3
w2                 602        12506         1063        >20.8

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.25 in the direction of the 
burst (Schlegel et al. 1998).