TITLE: GCN CIRCULAR NUMBER: 15082 SUBJECT: GRB 130807A: Swift detection of a GRB or Galactic transient DATE: 13/08/07 10:50:03 GMT FROM: David Palmer at LANL A. Melandri (INAF-OAB), D. N. Burrows (PSU), P. A. Evans (U Leicester), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL), M. H. Siegel (PSU), M. Stamatikos (OSU/NASA/GSFC) and R. L. C. Starling (U Leicester) report on behalf of the Swift Team: At 10:25:43 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 130807A (trigger=565651). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 269.801, -27.613 which is RA(J2000) = 17h 59m 12s Dec(J2000) = -27d 36' 44" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single-peaked structure with a duration of at least 30 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 10:27:08.2 UT, 85.0 seconds after the BAT trigger. Although a bright and variable source is apparent in the promptly downloaded light curve, the instrument did not centroid on the source in the initial 2.5-s promptly downloaded image, and the XRT stayed in WT mode for the remainder of the short first snapshot until Swift slewed away from the target. We therefore will have to wait until the second orbit to localize the XRT counterpart. UVOT took a finding chart exposure of 166 seconds with the U filter starting 145 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 25% of the BAT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the sub-image. The 8'x8' region for the list of sources generated on-board covers 100% of the BAT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the region. No correction has been made for the large, but uncertain extinction expected. Due to the proximity of this source to the Galactic center (3.3 degrees from the center) it is more likely that this is a Galactic source rather than a cosmological GRB. Determination of the nature of this source will require the full downlinked data. Burst Advocate for this burst is A. Melandri (andrea.melandri AT brera.inaf.it). 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.)