NOTE: uvot_fluxes_wget.pl vrs. 2020-11-03a fem at 210421d11h29m52s308002usUT
NOTE: Source region spec. is: 254.32596 42.56994 3"
NOTE: Used archived opt source position of 254.32596  42.56994  3.00
NOTE: position reference is GCN_Circulars-29845
NOTE: Possible detection in uu at T+50.8
NOTE: Possible detection in bb at T+75.4
NOTE: Possible detection in w1 at T+26.1 sum
NOTE: Possible detection in vv at T+125.9
NOTE: Possible detection in m2 at T+150.4 sum
WARNING: t_start for light curve (26) and t_start from the exposure report (2) do not agree.
  Replace ??? in draft Circular with correct value.

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

GRB 210420: Swift/UVOT Upper Limits

***UBS*** (***INSTITUTION***) and ***BA*** (***BA INSTITUTION***)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210420
***???*** s after the BAT trigger (***Author*** et al., GCN Circ. ????).
No optical afterglow consistent with the optical position
(Lipunov et al. GCN Circ. 29845)
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 initial exposures are:

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

v                  126          146          175         >17.2
b                   75           95          194         >17.7
u                   51           71          549         >16.7
w1                  26           46          156         >17.0
m2                 150          170           78         >17.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.022 in the direction of the burst
(Schlegel et al. 1998).


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

GRB 210420: Swift/UVOT Detection

***UBS*** (***INSTITUTION***) and ***BA*** (***BA INSTITUTION***)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210420
***???*** s after the BAT trigger (***Author*** et al., GCN Circ. ????).
A source consistent with the optical position
(Lipunov et al. GCN Circ. 29845)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  16:57:18.03 = 254.32512 (deg.)
    Dec (J2000) = +42:34:12.4  =  42.57011 (deg.)
with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence).

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

v                  126          146          175         17.39 +/- 0.08
b                   75           95          194         17.86 +/- 0.05
u                   51           71           19         17.16 +/- 0.16
w1                  26           46          156         17.25 +/- 0.09
m2                 150          170           78         17.70 +/- 0.20

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.022 in the direction of the burst
(Schlegel et al. 1998).