TITLE:   GCN CIRCULAR
NUMBER:  14002
SUBJECT: GRB 121125A: Swift/UVOT Detection
DATE:    12/11/26 22:17:56 GMT
FROM:    Frank Marshall at GSFC  <femarsha@khamseen.gsfc.nasa.gov>

F. E. Marshall (NASA/GSFC) and B. N. Barlow (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 121125A
75 s after the BAT trigger (Barlow et al., GCN Circ. 13993).
A source consistent with the XRT position
(Goad et al., GCN Circ. 13998) is detected in the initial UVOT exposures.

The refined UVOT position is:
    RA  (J2000) =  15:14:06.58 = 228.52740 (deg.)
    Dec (J2000) = +55:18:48.0  =  55.31332 (deg.)
with an estimated uncertainty of 0.50 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               75          225          147         16.35 +/- 0.03
v                 4693         4892          197         19.11 +/- 0.19
b                 4076         4276          197         19.31 +/- 0.13
u                  288          423          134         16.21 +/- 0.04
w1                5103         5302          197         20.06 +/- 0.32
m2                4897        11750         1082        >21.9
w2                4488         6123          393        >21.6

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.01 in the direction of the burst
(Schlegel et al. 1998).