NOTE: uvot_fluxes_wget.pl vrs. 2020-11-03a fem at 210820d21h05m02s046513usUT
NOTE: Source region spec. is: 20.63952 4.60783 3"
NOTE: Used archived uvot source position of  20.63952   4.60783  3.00
NOTE: position reference is GCN_Circ_30664
NOTE: A UVOT position was reported in GCN_Circ_30664
NOTE: Possible detection in uu at T+131.2
NOTE: Possible detection in bb at T+386.9
NOTE: Possible detection in vv at T+585.4 sum

=========== Draft Upper Limit Circular ========

GRB 210820A: Swift/UVOT Upper Limits

J. D. Gropp (PSU) and A. P. Beardmore (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210820A
131 s after the BAT trigger (Beardmore et al., GCN Circ. 30664).
No optical afterglow consistent with the XRT position
*** POSITION REFERENCE is GRB_Auto_Processing ***
is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

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

u_FC               131          381          246         >17.4
v                  437         1833          175         >18.3
b                  387         1782          192         >19.0
u                  131         1310          432         >17.8
w1                 784         1733           58         >19.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.030 in the direction of the burst
(Schlegel et al. 1998).


=========== Draft Detection Circular ========

GRB 210820A: Swift/UVOT Detection

J. D. Gropp (PSU) and A. P. Beardmore (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210820A
131 s after the BAT trigger (Beardmore et al., GCN Circ. 30664).
A source consistent with the XRT position
*** POSITION REFERENCE is GRB_Auto_Processing ***
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  01:22:33.48 =  20.63952 (deg.)
    Dec (J2000) = +04:36:28.3  =   4.60786 (deg.)
with an estimated uncertainty of 0.45 arc sec. (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

v                  437         1684          156         18.86 +/- 0.24
b                  387          555           39         18.57 +/- 0.19
u                  131          381          246         17.60 +/- 0.06
w1                 784         1733           58        >19.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.030 in the direction of the burst
(Schlegel et al. 1998).