TITLE: GCN CIRCULAR NUMBER: 15099 SUBJECT: GRB 130816B: Swift detection of a burst DATE: 13/08/16 05:06:44 GMT FROM: Michael Stamatikos at OSU/GSFC M. Stamatikos (OSU/NASA/GSFC), P. D'Avanzo (INAF-OAB), M. H. Siegel (PSU) and T. N. Ukwatta (MSU) report on behalf of the Swift Team: At 04:53:38 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 130816B (trigger=566561). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 170.093, -57.558 which is RA(J2000) = 11h 20m 22s Dec(J2000) = -57d 33' 28" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single peak structure with a duration of about 20 sec. The peak count rate was ~2440 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 04:54:48.8 UT, 70.2 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 170.01845, -57.55829 which is equivalent to: RA(J2000) = 11h 20m 04.43s Dec(J2000) = -57d 33' 29.8" with an uncertainty of 3.9 arcseconds (radius, 90% containment). This location is 143 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. We cannot determine whether the source is fading at the present time. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 4.04 x 10^21 cm^-2 (Kalberla et al. 2005). UVOT took a finding chart exposure of 150 seconds with the White filter starting 75 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 none of the XRT error circle. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT 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. Burst Advocate for this burst is M. Stamatikos (Michael.Stamatikos-1 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.)