TITLE:   GCN CIRCULAR
NUMBER:  15032
SUBJECT: GRB 130725B: Swift/UVOT Detection of an Optical Counterpart
DATE:    13/07/25 21:56:37 GMT
FROM:    Mike Siegel at PSU/Swift MOC  <siegel@swift.psu.edu>

M. H Siegel and C. A. Swenson (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 130725B
72 s after the BAT trigger (Swenson et al., GCN Circ. 15029).
A source consistent with the XRT position
(Swenson et al. GCN Circ. 15029)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
  RA  (J2000) =  14:16:57.76 = 214.24068 (deg.)
  Dec (J2000) = -11:07:41.8  = -11.12827 (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               72          221          147         17.29 +/- 0.03
u                  284          534          246         17.96 +/- 0.07

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.061 in the direction of the burst
(Schlegel et al. 1998).