GCN Circular 3779

E.S. Rykoff, W. Rujopakarn, S.A. Yost, F. Yuan (U Mich) report on behalf 
of the ROTSE collaboration:

ROTSE-IIIa, located at Siding Spring Observatory, Australia, responded 
to GRB 050807 (HETE trigger 3889).  The initial response was delayed due 
to confusion with the different coordinates received in the first two 
GCN notices.  Targeted observations of the updated GCN position (trigger 
3889;3) began at 11:09:51.5 UT, 11.1 minutes after the burst, under 
excellent conditions.  We took 10 5-sec, 10 20-sec and 35 60-sec 
exposures.  These unfiltered images are calibrated relative to USNO A2.0.

The final ground error box (trigger 3889;5) is entirely contained within 
the initial targeted observation.  Comparison to the DSS (second epoch) 
reveals no new sources within the 3-sigma error box, for both single 
images and coadding into sets of 10. Individual images have limiting 
magnitudes ranging from 16.3-17.5; we set the following specific limits.

start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------
11:09:51.5   11:12:7.4     136        17.7   666               Y
11:12:16.8   11:16:55.1    284        18.2   812               Y
11:17:9.9    11:28:34.3    684        18.5   1105              Y