TITLE: GCN CIRCULAR NUMBER: 15246 SUBJECT: GRB 130925A: Swift detection of a burst DATE: 13/09/25 04:26:41 GMT FROM: David Palmer at LANL A. Y. Lien (NASA/GSFC/ORAU), C. B. Markwardt (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL), J. L. Racusin (NASA/GSFC), M. H. Siegel (PSU) and T. N. Ukwatta (MSU) report on behalf of the Swift Team: At 04:11:24 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 130925A (trigger=571830). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 41.183, -26.134 which is RA(J2000) = 02h 44m 44s Dec(J2000) = -26d 08' 03" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed that the burst was active during the pre-planned slew before the nominal trigger with an additional peak extending at least to T+170. The peak count rate was ~2700 counts/sec (15-350 keV), at ~110 sec after the trigger. The XRT began observing the field at 04:13:52.3 UT, 147.4 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 41.1766, -26.1544 which is equivalent to: RA(J2000) = +02h 44m 42.38s Dec(J2000) = -26d 09' 15.8" with an uncertainty of 5.1 arcseconds (radius, 90% containment). This location is 76 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. UVOT took a finding chart exposure of 150 seconds with the White filter starting 156 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. Results from the list of sources generated on-board are not available at this time. No correction has been made for the expected extinction corresponding to E(B-V) of 0.02. Burst Advocate for this burst is A. Y. Lien (yarleen AT gmail.com). 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.)