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GCN Circular 6729

GRB 070809: ROTSE-III Optical Limits
2007-08-09T19:56:11Z (17 years ago)
Eli Rykoff at U of Michigan/ROTSE <>
E.S. Rykoff (U Mich), F. Yuan (U Mich), C. Akerlof (U Mich), H. Swan (U Mich), 
B. E. Schaefer (Louisiana State), R. Quimby (U Texas), report on behalf of the 
ROTSE collaboration:

  ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia, responded 
to GRB 070809 (Swift trigger 287344; Marshall, et al., GCN 6728), producing 
images beginning 10.2 s after the GCN notice time. An automated response took 
the first image at 19:22:48.2 UT, 30.9 s after the burst, under excellent 
conditions. We took 10 5-sec, 10 20-sec and 10 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 or the XRT error circle, for both single images and 
coadding into sets of 10. Individual images have limiting magnitudes ranging 
from 15.8-17.4; we set the following specific limits.

  start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
  19:22:48.2   19:22:53.2         5     16.1           30.9       N
  19:22:48.2   19:24:06.2        78     17.5           30.9       Y
  19:24:19.9   19:29:06.8       286     18.1          122.6       Y
  19:29:16.6   19:40:41.9       685     18.4          419.3       Y
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