TITLE:   GCN CIRCULAR
NUMBER:  13797
SUBJECT: GRB 120923A: ROTSE-III Optical Limits 
DATE:    12/09/23 05:41:38 GMT
FROM:    Weikang Zheng at U.of Michigan  <zwk@umich.edu>

W. Zheng (U Mich) and T. Guver (Sabanci U) report on behalf of the ROTSE
collaboration: 

ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB 120923A
(Swift trigger 534402; Yershov et al., GCN 13796), producing images
beginning 0.7 s after the GCN notice time. An automated response took the
first image at 05:17:43.7 UT, 97.4 s after the burst, under fair conditions.
We took 10 5-sec, 10 20-sec and 0 60-sec exposures. These unfiltered images
are calibrated relative to USNO A2.0 (R). Imaging is on going. 

Comparison to the DSS (second epoch) reveals no new sources within the
3-sigma Swift/BAT error circle. Individual images have limiting magnitudes
ranging from 15.4-16.3; we set the following specific limits. 

start UT       end UT      t_exp(s)   mlim     Coadd?

------------------------------------------------------

05:17:43     05:17:48           5      15.6        N

05:17:55     05:18:00           5      15.4        N

05:18:07     05:18:12           5      15.7        N

05:17:43     05:19:31           50     16.4        Y