TITLE:   GCN CIRCULAR
NUMBER:  20306
SUBJECT: GRB 161219B: Swift/UVOT Detection
DATE:    16/12/20 17:08:41 GMT
FROM:    Frank Marshall at GSFC  <femarsha@khamseen.gsfc.nasa.gov>

F. E. Marshall (NASA/GSFC) and A. D'Ai (INAF-IASFPA)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 161219B
112 s after the BAT trigger (D'Ai et al., GCN Circ. 20296).
A source consistent with the XRT position
(Beardmore et al. GCN Circ. 20297)
is detected in the initial UVOT exposures.

The source is detected in the first white exposure at the position:
  RA(J2000)  =	06:06:51.43 =  91.71428
  DEC(J2000) = -26:47:29.5  = -26.79152
with an uncertainty of 0.42" (90% confidence)

Preliminary detections using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are
in the table below. Fading is seen in all filters.
The detection in the w2 filter is consistent
with a  relatively low redshift as suggested by
Kruehler et al. (GCN Circ. 20299).

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag
white              112          261          147         16.1 +/- 0.1
v                  653          673           19         16.7 +/- 0.2
b                  579          599           20         16.9 +/- 0.1
u                  324          573          246         16.0 +/- 0.1
u                44962        45868          875         18.0 +/- 0.1 
w1                 702          722           20         15.6 +/- 0.1
m2                 677          697           19         15.7 +/- 0.2
w2                 629          649           20         15.9 +/- 0.2

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.