TITLE:   GCN CIRCULAR
NUMBER:  34665
SUBJECT: GRB 230911C: Swift/UVOT Upper Limits
DATE:    23/09/11 20:49:01 GMT
FROM:    Alice Breeveld at MSSL-UCL <a.breeveld@ucl.ac.uk>

A. A. Breeveld (UCL-MSSL) and E. Sonbas (Adiyaman Univ.) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 230911C 122 s after the BAT trigger (Sonbas et al., GCN Circ. 34655).
No optical afterglow consistent with the XRT position (Evans et al., GCN Circ. 34658) 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

white_FC           122          272          147         >20.4
white              122         4926          289         >21.0
u_FC               280          530          246         >19.7
u                  280         4572          708         >20.2
b                  537         4778          235         >19.8
w1                 661         4368          216         >19.0
w2                 587          781           39         >18.2

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.101 in the direction of the burst (Schlegel et al. 1998).