TITLE:   GCN CIRCULAR
NUMBER:  33471
SUBJECT: GRB 230307A: Swift/UVOT detection
DATE:    23/03/13 15:54:52 GMT
FROM:    Alice Breeveld at MSSL-UCL  <a.breeveld@ucl.ac.uk>

A. A. Breeveld (UCL-MSSL), and C. Salvaggio (INAF-OAB) report on behalf 
of the Swift/UVOT team:

The Swift/UVOT began observations of the field of GRB 230307A 99.5 ks 
after the Fermi/GBM-detected trigger (Dalessi et al., GCN 33407).
A fading source consistent with the enhanced XRT position (Burrows et 
al., GCN 33465) and consistent with the optical counterpart reported by 
Levan et al. (GCN 33439), Lipunov et al. (GCN 33441), Fulton et al. (GCN 
33443), O'Connor et al. (GCN 33447), Im et al. (GCN 33449), Vanderspek 
et al. (GCN 33453) and Bom et al. (GCN 33459) is detected in the initial 
UVOT exposures. Detections and 3 sigma upper limits are given in the 
following table:

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

white        99525      110441      2265     21.28 +/- 0.16
white       133031      208070      2931     22.09 +/- 0.32
white       212899      420530      3418    >22.25
u            83621       88252       422    >20.44

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.084 in the direction of 
the burst (Schlegel et al. 1998).