TITLE:   GCN CIRCULAR
NUMBER:  6393
SUBJECT: GRB 070509: ROTSE-III Optical Limits 
DATE:    07/05/09 03:14:54 GMT
FROM:    Eli Rykoff at U of Michigan/ROTSE  <erykoff@umich.edu>

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

ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia, 
responded to GRB 070509 (Swift trigger 278903), producing images 
beginning 7.4 s after the GCN notice time. An automated response took 
the first image at 02:56:22.4 UT, 475.1 s after the burst, under fair 
conditions. We took 10 5-sec, 10 20-sec and continuing 60-sec exposures. 
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. Individual images have limiting magnitudes 
ranging from 15.2-16.2; we set the following specific limits.

start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------
02:56:22.4   02:56:27.4         5     15.3          475.1       N
02:56:22.4   02:57:39.6        77     16.6          475.1       Y
02:57:53.8   03:02:39.5       285     17.2          566.5       Y