GCN Circular 13805
A. A. Breeveld (MSSL-UCL), V. N. Yershov (MSSL-UCL) and N. P. M. Kuin (MSSL-UCL) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 120923A 143 s after the BAT trigger (Yershov et al., GCN Circ. 13796). No optical afterglow consistent with the XRT or Gemini position (Goad et al., GCN Circ. 13801, Levan et al., GCN Circ. 13802) is detected in the initial UVOT exposure. A preliminary 3-sigma upper limit using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart exposure is: Filter T_start(s) T_stop(s) Exp(s) Mag white 143 293 147 >21.3 The magnitude in the table is not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.16 in the direction of the burst (Schlegel et al. 1998).