TITLE: GCN CIRCULAR NUMBER: 14620 SUBJECT: GRB 130511A: Swift detection of a burst with an optical counterpart DATE: 13/05/11 11:42:24 GMT FROM: David Palmer at LANL H. A. Krimm (CRESST/GSFC/USRA), D. N. Burrows (PSU), N. Gehrels (NASA/GSFC), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 11:30:47 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 130511A (trigger=555600). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 196.639, +18.698 which is RA(J2000) = 13h 06m 33s Dec(J2000) = +18d 41' 51" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single short peak of duration ~0.5 sec followed by a 10-second tail. The peak count rate was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 11:31:58.9 UT, 71.6 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 196.64698, 18.70893 which is equivalent to: RA(J2000) = 13h 06m 35.28s Dec(J2000) = +18d 42' 32.1" with an uncertainty of 3.6 arcseconds (radius, 90% containment). This location is 47 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (2.08 x 10^20 cm^-2, Kalberla et al. 2005), with an excess column of 2.5 (+1.47/-1.33) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 74 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 13:06:34.96 = 196.64567 DEC(J2000) = +18:42:36.0 = 18.70999 with a 90%-confidence error radius of about 0.64 arc sec. This position is 7.0 arc sec. from the center of the XRT error circle. The estimated magnitude is 19.18 with a 1-sigma error of about 0.15. No correction has been made for the expected extinction corresponding to E(B-V) of 0.03. Burst Advocate for this burst is H. A. Krimm (krimm AT milkyway.gsfc.nasa.gov). 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.)