TITLE:   GCN CIRCULAR
NUMBER:  8293
SUBJECT: GRB 080928A: ROTSE-III Confirmation of Optical Counterpart 
DATE:    08/09/28 15:58:35 GMT
FROM:    Eli Rykoff at UCSB  <erykoff@physics.ucsb.edu>

E.S. Rykoff (UCSB), F. Yuan (U Mich), T.A. McKay (U Mich), report on 
behalf of the ROTSE collaboration:

ROTSE-IIIa, located at Siding Spring Observatory, Australia, responded 
to GRB 080928A (Swift trigger 326115, GCN 8292, Sakamoto et al.). The 
first image was at 15:03:44.9 UT, 132.0 s after the burst (7.9 s after 
the GCN notice time). The unfiltered images are calibrated relative to 
USNO A2.0. Our initial images did not detect the UVOT counterpart to a 
limiting magnitude of ~17.2.  However, after ~500 seconds the source 
brightened to 16.9 mag, and it brightened again at ~2000 s to ~16.2 mag. 
The coordinates of the source are consistent with the UVOT counterpart:

      06:20:17.0      -55:11:58.8    (J2000), with positional 
uncertainty of 1" or better

start UT    	mag     mlim(of image)
----------------------------------
15:19:02.3     16.9     16.9


This source is not visible in DSS (second epoch), 2MASS or the MPChecker 
database.

A jpeg image is available at 
http://www.rotse.net/images/gsb326115_3a04_img.jpg

Continuing observations are in progress.