TITLE:   GCN CIRCULAR
NUMBER:  18546
SUBJECT: GRB 151031A: Swift/UVOT Detection
DATE:    15/10/31 22:42:11 GMT
FROM:    Paul Kuin at MSSL  <npkuin@gmail.com>

N. P. M. Kuin (UCL-MSSL) and E. Sonbas (Adiyaman Univ.) report on
behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 151031A
439 s after the BAT trigger (Sonbas et al., GCN Circ. 18538). A source
at the VLT position (Malesani et al, GCN Circ. 18540) and consistent with
the XRT position (Evans et al. GCN Circ. 18541) is detected in the initial
UVOT exposures.

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              439         1020          314         20.63 +/- 0.16
v                  595         8257          627        >20.1
b                  695         7642          588        >20.2
u                  670         7437          430         20.34 +/- 0.28
w1                 645         8677          635        >20.0
m2                 620         8462          627        >20.0
w2                 746         8053          607        >21.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.03 in the direction of the burst
(Schlegel et al. 1998).