GCN Circular 3978

S.A. Yost, E.S. Rykoff (U Mich), B. Schaefer (Louisiana State), D.A. 
Smith (Guilford), T. Guver (U. Istanbul) report on behalf of the ROTSE 
collaboration:

ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB 
050915 (Swift trigger 155242), producing images beginning 7.5 s after 
the GCN notice time. An automated response took the first image at 
11:23:10.5 UT, 28.2 s after the burst, under fair conditions. We took 
10 5-sec, 10 20-sec and 20 60-sec eposures. These unfiltered images are 
calibrated relative to USNO A2.0 (R). With the arrival of morning 
twilight, few further images are expected.

Comparison to the DSS (second epoch) reveals no new sources within the 
3-sigma error circle, for both single images and coadding into sets of 
10. Individual images have limiting magnitudes ranging from 16.0-17.4; 
we set the following specific limits.

start UT 		end UT 	t_exp(s) 	mlim 	t_start-tGRB(s) Coadd?
--------------------------------------------------------------------
11:23:10.5 	11:24:32.5 	82 	17.4 		28.2		 Y
11:24:33.4 	11:29:34.4 	301 	18.0 		111.1 	 Y