TITLE:   GCN CIRCULAR
NUMBER:  8362
SUBJECT: GRB 081012: ROTSE-III Optical Limits
DATE:    08/10/12 14:54:25 GMT
FROM:    Fang Yuan at ROTSE  <yuanfang@umich.edu>

F. Yuan (U Mich) report on behalf of the ROTSE collaboration:

ROTSE-IIIa, located at Siding Spring Observatory, Australia, responded  
to GRB 081012 (Swift trigger 331475, GCN 8361, Stroh et al. ),  
producing images beginning 7.2s after the GCN notice time. An  
automated response took the first image at 13:11:03.2 UT, 39.3s after  
the burst. Early observations were affected by proximity to the full  
moon and the first usable image started at 13:27:03.0 UT, ~1000s after  
the burst. We took over 100 20s 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, for both single images and coadding  
into sets of 10. Individual images have limiting magnitudes ranging  
from 15.8-16.2; we set the following specific limits.

start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------
13:27:03.0   13:27:23.0        20     15.8             999       N
13:28:01.3   13:32:42.9       281     17.4          1057       Y