[vsnet-grb-info 20966] GRB 180728A: Swift/UVOT Detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23064
SUBJECT: GRB 180728A: Swift/UVOT Detection
DATE:    18/07/31 03:04:49 GMT
FROM:    Sam LaPorte at PSU  <sjl5346 at psu.edu>

GRB 180728A: Swift/UVOT Detection

S. J. LaPorte (PSU) and R. L. C. Starling (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180728A
1740 s after the BAT trigger (Starling et al., GCN Circ. 23046).
A source consistent with the enhanced XRT position
(Osborne et al. GCN Circ. 23051)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  16:54:15.53 =  253.56472 (deg.)
    Dec (J2000) = -54:02:40.2 =  -54.04451 (deg.)
with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence),
consistent with MASTER OT J165415.75-540239.27 (Lipunov et al., GCN #23050).

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             1740         1890          147         16.25 +/- 0.03
white             7713         15148         465         17.28 +/- 0.03 
v                 1897         1917           20         16.07 +/- 0.14
b                 1995         2013           18         16.58 +/- 0.10
u                 1970         1990           20         15.93 +/- 0.10
w1                1946         1966           20         16.20 +/- 0.17
m2                1921         2114           39         16.60 +/- 0.18
w2                2045         2065           19         16.37 +/- 0.19

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.29 in the direction of the burst
(Schlegel et al. 1998).