GCN Circular 7349

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

ROTSE-IIIa, located at Siding Spring Observatory, Australia, responded to 
GRB 080303A (Swift trigger 304549), producing images beginning 8.4 s after 
the GCN notice time. An automated response took the first image at 
09:10:55.3 UT, 20.0 s after the burst, and during the gamma-ray emission, 
under twilight 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; the field is not crowded. Individual 
images have limiting magnitudes ranging from 13.3-15.8, with the poor 
limits at the start due to the bright twilight that was rapidly fading.  
We set the following specific limits.

start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------
09:10:55.4   09:11:00.4         5     13.3           20.1       N
09:10:55.4   09:13:06.9       131     14.1           20.1       Y
09:21:35.1   09:29:30.1       475     16.2          659.8       Y