TITLE:   GCN CIRCULAR
NUMBER:  6719
SUBJECT: GRB 070808: ROTSE-III Optical Limits
DATE:    07/08/08 19:12:22 GMT
FROM:    Brad Schaefer at LSU  <schaefer@grb.phys.lsu.edu>

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

ROTSE-IIIa, located at Siding Spring Observatory, Australia, responded to
GRB 070808 (Swift trigger 287260; J. R. Cummings et al., GCN 6718),
producing images beginning 7.6 s after the GCN notice time. An automated
response took the first image at 18:28:29.6 UT, 29.0 s after the burst,
under excellent conditions. We took 10 5-sec, 10 20-sec and 10 60-sec
exposures, with further exposures ongoing. 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 or the XRT error circle; the field is not 
crowded. Individual images have limiting magnitudes ranging from 
16.2-17.6; we set the following specific limits.

start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------
18:28:29.6   18:28:34.6         5     16.2           29.0       N