GCN Circular 22565

S.W.K. Emery (UCL-MSSL) and J. L. Racusin (NASA/GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180329B
113 s after the BAT trigger (Racusin et al., GCN Circ. 22558
Not found
 
 
).
A fading source consistent with the XRT position
(Beardmore et al. GCN Circ. 22559
Not found
 
 
) also detected by the
NOT (Perley et al. GCN Circ. 22562
Not found
 
 
) and RATIR (Watson et al. GCN Circ. 22564
Not found
 
 
)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  05:31:36.91 =  82.90381 (deg.)
    Dec (J2000) = -23:41:25.8  = -23.69051 (deg.)
with an estimated uncertainty of 0.43 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              113          263          147         17.69 +/- 0.04
white              550         6892          599         17.64 +/- 0.03
v                  601         5867          274         17.25 +/- 0.07
b                  526         6687          452         17.94 +/- 0.05
u                  271         6482          697         17.00 +/- 0.04
u                16039        39219         1961         18.74 +/- 0.07
w1                 650         6277          452         18.72 +/- 0.14
m2                 626         6073          274        >19.8
w2                 577         7017          390        >20.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.04 in the direction of the burst
(Schlegel et al. 1998).