TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3978 SUBJECT: GRB 050915: ROTSE-III optical limits DATE: 05/09/15 12:09:48 GMT FROM: Sarah Yost at U.Michigan 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