[vsnet-grb-info 24594] GRB 200107B: Swift/UVOT Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26693
SUBJECT: GRB 200107B: Swift/UVOT Observations
DATE:    20/01/09 22:28:12 GMT
FROM:    Frank Marshall at Swift/UVOT  <marshall at milkyway.gsfc.nasa.gov>

F.E. Marshall (NASA/GSFC) and M. G. Bernardini (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 200107B
903 s after the BAT trigger (Bernardini et al., GCN Circ. 26661).
Some of the exposures are affected by poor attitude control,
but we have selected observing times for which this is not
a significant issue. A source consistent with the position of the optical  
source reported by Lipunov (GCN Circ. 26660) is weakly detected (2.6 sigma)
in the initial UVOT exposure.

The preliminary detection 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_FC           903         1052           55         19.3 (+0.5/-0.4)
v                 1059         1079           19        >18.6
b                 1157         1177           19        >18.6
u                 1133         3144          179        >19.7
w1                2777         2976          197        >19.5
w2                1208         1228           19        >18.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.19 in the direction of the burst
(Schlegel et al. 1998).