TITLE: GCN CIRCULAR NUMBER: 11261 SUBJECT: GRB 100909A: Swift target of opportunity observation DATE: 10/09/09 13:04:56 GMT FROM: Mike Siegel at PSU/Swift MOC M. H. Siegel (PSU), S. D. Barthelmy (GSFC), M. M. Chester (PSU), P. A. Evans (U Leicester), J. M. Gelbord (PSU), J. A. Kennea (PSU), K. L. Page (U Leicester) and R. L. C. Starling (U Leicester) report on behalf of the Swift Team: Swift began a target of opportunity observation of GRB 100909A on September 9, 2010 at 12:18 UT, approximately 3.2 hours after the burst was detected by INTEGRAL. Swift data for these observations utilize Target ID 20147. The XRT began observing the field at 12:19:37.4 UT, 11.7 ks after the INTEGRAL trigger. In 1.8 ks of promptly downlinked data there is a faint source, detected at the 3.2-sigma level at: RA, Dec= 73.94797, +54.65798 which is equivalent to: RA (J2000) : 04h 55m 47.51s Dec (J2000): +54d 39' 28.7'' with an estimated uncertainty of 6 arcsec (radius, 90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 11687 seconds after the INTEGRAL trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 44% of the INTEGRAL error circle and 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The coverage of the INTEGRAL and XRT error circles by the 8'x8' region for the list of sources generated on-board is uncertain because the large number of sources filled the available telemetry. No correction has been made for the expected extinction corresponding to E(B-V) of 0.51. Burst Advocate for this burst is M. H. Siegel (siegel AT astro.psu.edu). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.)