TITLE:   GCN CIRCULAR
NUMBER:  18529
SUBJECT: GRB 151027B: Swift UVOT detection
DATE:    15/10/29 15:34:43 GMT
FROM:    Alice Breeveld at MSSL-UCL  <a.breeveld@ucl.ac.uk>

A. A. Breeveld (UCL-MSSL) and T. N. Ukwatta (LANL) report on behalf of
the Swift/UVOT team:

In Swift/UVOT followup observations of GRB 151027B (Ukwatta et al., GCN 
Circ. 18499) a source is found in the summed up V filter exposures at a 
position consistent with the XRT (Osborne et al., GCN Circ. 18504) and 
the optical/NIR counterparts reported by Malesani et al. GCN Circ. 
18501, Xu et al. GCN Circ. 18505, Wiseman and Greiner GCN Circ. 18507, 
Buckley et al. GCN Circ. 18511, Watson et al. GCN Circ. 18512, and 
Dichiara et al. GCN Circ. 18520.

A preliminary detection using the UVOT photometric system (Breeveld et 
al. 2011, AIP Conf. Proc. 1358, 373) for V data taken in the first and 
second segment is:

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

v                     191       28529     1986   20.8 ± 0.3

The magnitudes in the table are not corrected for the strong Galactic
extinction due to the reddening of E(B-V) = 0.25 in the direction of the 
burst (Schlegel et al. 1998).