GCN Circular 14370

A. Breeveld (MSSL/UCL) and A. Y. Lien (NASA/GSFC/ORAU) report on behalf 
of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 130408A 
134 s after the BAT trigger (Lien et al., GCN Circ. 14361
Not found
 
 
). A bright but 
rapidly fading source is detected in the initial exposures (Siegel and 
Lien, GCN Circ. 14363
Not found
 
 
) with a position consistent with detections by 
Melandri et al., (GCN Circ., 14362), Sudilovsky et al., (GCN Circ., 
14364) and Beardmore et al., (GCN Circ. 14367
Not found
 
 
).

The preliminary UVOT position is:
  RA(J2000)  =    08:57:37.30 = 134.40540
  DEC(J2000) =   -32:21:38.9  = -32.36081
with a 90%-confidence error radius of about 0.5 arc sec.

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

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white              156          305      147.4          16.80 � 0.05
white             3708         3900      189.2          20.29 � 0.22
white             6083        10367      924.3          21.99 � 0.35
v                  134          145       10.1          15.75 � 0.15
v                 4201         4400      196.7          19.61 � 0.35
b                 3503         6078      393.2          >20.84
u                  313         5872      236.2          >20.55
uvw1              4611         4752      139.0          >19.82
uvm2              4405         4605      196.6          >19.75
uvw2              3996        21851     1748.0          >21.56

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.258 in the direction of 
the burst (Schlegel et al. 1998).