GCN Circular 14384

N. P. M. Kuin and M. De_Pasquale (UCL-MSSL) report on behalf of
the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 130418A
138 s after the BAT trigger (De_Pasquale et al., GCN Circ. 14377
Not found
 
 
).
A source consistent with the XRT position (De Pasquale et al.
GCN Circ. 14377
Not found
 
 
) is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  09:56:08.88 = 149.03700 (deg.)
    Dec (J2000) = +13:40:02.7  =  13.66741 (deg.)
with an estimated uncertainty of 0.50 arc sec. (radius, 90% confidence).

Preliminary detections 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          288          146         14.85 +/- 0.05

u                  296          353           56         14.71 +/- 0.04
v                 5634         5834          197         17.69 +/- 0.08
b                 3567         3766          197         17.41 +/- 0.05
w1                6044         6124           78         17.25 +/- 0.11
m2                5839         6039          197         17.61 +/- 0.11
w2                5430         5630          197         18.08 +/- 0.11

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.03 in the direction of the burst
(Schlegel et al. 1998).

Due to a Moon constraint, Swift observations will stop for now. Continuing
acquisition of ground-based data, including ubv photometry will be useful
at this time.