TITLE: GCN CIRCULAR NUMBER: 10979 SUBJECT: GRB 100725A: Swift detection of a burst DATE: 10/07/25 07:23:01 GMT FROM: David Palmer at LANL C. B. Markwardt (CRESST/GSFC/UMD), J. M. Gelbord (PSU), V. Mangano (INAF-IASFPA), K. L. Page (U Leicester), D. M. Palmer (LANL), T. A. Pritchard (PSU) and B. Sbarufatti (INAF-OAB/IASFPA) report on behalf of the Swift Team: At 07:12:52 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 100725A (trigger=429954). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 166.515, -26.688 which is RA(J2000) = 11h 06m 04s Dec(J2000) = -26d 41' 14" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi-peaked structure with a duration of at least 40 sec. The peak count rate was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 07:14:09.1 UT, 76.7 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 166.4839, -26.6716 which is equivalent to: RA(J2000) = 11h 05m 56.13s Dec(J2000) = -26d 40' 17.7" with an uncertainty of 5.4 arcseconds (radius, 90% containment). This location is 115 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. The initial flux in the 2.5 s image was 1.32e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of nominal 150 seconds with the White filter starting 84 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. Data from the 2.7'x2.7' sub-image are not available at this time. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.05. Burst Advocate for this burst is C. B. Markwardt (Craig.Markwardt AT 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.)