TITLE:   GCN CIRCULAR
NUMBER:  28311
SUBJECT: GRB 200829A: Swift/UVOT Detection
DATE:    20/08/29 19:10:29 GMT
FROM:    Paul Kuin at MSSL  <npkuin@gmail.com>

N.P.M. Kuin (MSSL-UCL) and M. H. Siegel (PSU) report on behalf of
the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 200829A
138 s after the BAT trigger (Siegel et al., GCN Circ. 28307).
The UV-optical source position is RA=251.204709, Dec=72.329356 deg
(J2000) which is in sexagesimal:
RA(J2000) = 16h 44m 49.14s
Dec(J2000) = 72d 19' 45.63"
with a positional uncertainty of 0.35" 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              138          288          147         14.29 +/- 0.02
white              576          596           19         15.43 +/- 0.04
white             1527         1547           19         16.38 +/- 0.06
v                  626          646           19         15.50 +/- 0.10
b                  552          572           19         15.68 +/- 0.07
u                  296          546          246         14.54 +/- 0.03
u                  700          720           19         15.12 +/- 0.07
w1                 675          696           19         15.19 +/- 0.12
m2                1080         1100           19         16.25 +/- 0.25
w2                1032         1398           39         17.64 +/- 0.30

Note that the times are since the BAT trigger time. The main burst took
place around 60s earlier during a Swift Slew.

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.04 in the direction of the burst
(Schlegel et al. 1998).