TITLE: GCN CIRCULAR NUMBER: 15088 SUBJECT: GRB 130812A: Swift detection of a burst DATE: 13/08/12 22:38:46 GMT FROM: Scott Barthelmy at NASA/GSFC V. D'Elia (ASDC), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), N. Gehrels (NASA/GSFC), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), V. Mangano (PSU), C. B. Markwardt (NASA/GSFC) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 22:22:52 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 130812A (trigger=566228). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 92.402, -13.295 which is RA(J2000) = 06h 09m 37s Dec(J2000) = -13d 17' 42" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows multiple peaks with a total duration of about 10 sec. The peak count rate was ~4500 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 22:24:09.6 UT, 77.0 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 92.3955, -13.2875 which is equivalent to: RA(J2000) = 06h 09m 34.92s Dec(J2000) = -13d 17' 15.1" with an uncertainty of 2.1 arcseconds (radius, 90% containment). This location is 35 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 (1.51 x 10^21 cm^-2, Kalberla et al. 2005), with an excess column of 1.5 (+1.52/-1.37) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 250 seconds with the U filter starting 138 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 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.2 mag. 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 18.0 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.23. Burst Advocate for this burst is V. D'Elia (delia AT asdc.asi.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.)