TITLE:   GCN CIRCULAR
NUMBER:  6356
SUBJECT: GRB 070429: ROTSE-III Optical Limits 
DATE:    07/04/29 01:57:07 GMT
FROM:    Eli Rykoff at U of Michigan/ROTSE  <erykoff@umich.edu>

E.S. Rykoff (U Mich), B. E. Schaefer (Louisiana State), H. Swan (U 
Mich), report on behalf of the ROTSE collaboration:

ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia, 
responded to GRB 070429 (Swift trigger 277571, GCN 6355, Barthelmy, et 
al), producing images beginning 6.7 s after the GCN notice time. An 
automated response took the first image at 01:36:46.7 UT, 96.6 s after 
the burst, under good conditions. We took 10 5-sec, 10 20-sec exposures; 
imaging is ongoing. These unfiltered images are calibrated relative to 
USNO A2.0 (R).

Comparison to the DSS (second epoch) reveals no new sources within the 
3-sigma BAT error circle or the XRT error circle, for both single images 
and coadding into sets of 10; however, we are limited as the field is 
somewhat crowded. Individual images have limiting magnitudes ranging 
from 16.1-17.1; we set the following specific limits.

start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------
01:36:46.7   01:36:51.7         5     16.2           96.6       N
01:36:46.7   01:38:04.4        77     17.3           96.6       Y
01:38:19.4   01:43:08.1       288     18.0          189.3       Y