GCN Circular 19921

F. E. Marshall (NASA/GSFC) and J. K. Cannizzo (NASA/UMBC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 160912A
138 s after the BAT trigger (Cannizzo et al., GCN Circ. 19912
Not found
 
 
).
There is a weak detection of a source consistent with the XRT position
(Beardmore et al., GCN Circ. 19915
Not found
 
 
) and the optical afterglow
positions (Tanvir and Levan, GCN Circ. 19918
Not found
 
 
; Mazaeva et al., GCN Circ. 19919
Not found
 
 
)
in the initial UVOT exposures. There is little evidence for
variability.

The preliminary UVOT position is:
   RA  (J2000) =  20:05:59.74  = 301.49893 (deg.)
   Dec (J2000) =  +57:33:56.0  =  57.56555 (deg.)
with an estimated uncertainty of 1.0 arcsec. (radius, 90% confidence).

Preliminary detections and 2-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              138         8135          883         22.03 +/- 0.27
v                  626         7110          411         20.60 +/- 0.44
b                  552         7931          584        >22.14
u                  296         7726          814        >21.92
w1                 675         7520          588        >21.25
m2                 650         7314          391        >20.75
w2                 602         8215          484        >21.05

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.20 in the direction of the burst
(Schlegel et al. 1998).