[vsnet-grb-info 17381] GRB 151228B: Swift/UVOT Detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18766
SUBJECT: GRB 151228B: Swift/UVOT Detection
DATE:    15/12/30 07:45:04 GMT
FROM:    Alice Breeveld at MSSL-UCL  <a.breeveld at ucl.ac.uk>

A.A. Breeveld (UCL-MSSL), S.W.K. Emery (UCL-MSSL) and A.Y. Lien 
(GSFC/UMBC) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 151228B
49 s after the BAT trigger (Lien et al., GCN Circ. 18739).
A fading source consistent with the XRT position (Goad et al. GCN Circ. 
18743) is detected in the initial UVOT exposures in the white filter.

The preliminary UVOT position is:
     RA  (J2000) =  22:57:41.87 = 344.42446 (deg.)
     Dec (J2000) = +08:04:53.7  =   8.08159 (deg.)
with an estimated uncertainty of 0.58 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               70          220          147         19.62 ± 0.19
v                   49         6132          306        >19.2
b                  537         5514          274        >20.0
u                  282         5309          520        >20.1
w1                 661         6373          303        >20.1
m2                6137         6337          197        >19.9
w2                1386         5927          216        >20.8

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.06 in the direction of the 
burst (Schlegel et al. 1998).