TITLE: GCN CIRCULAR NUMBER: 15283 SUBJECT: GRB 131002A: Swift detection of a burst DATE: 13/10/02 07:49:31 GMT FROM: Caryl Gronwall at PSU/Swift-UVOT B. N. Barlow (High Point University), V. D'Elia (ASDC), P. A. Evans (U Leicester), C. Gronwall (PSU), A. Y. Lien (NASA/GSFC/ORAU), D. Malesani (DARK/NBI), F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester), T. Sakamoto (AGU), M. H. Siegel (PSU) and M. C. Stroh (PSU) report on behalf of the Swift Team: At 06:54:21 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 131002A (trigger=572721). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 253.275, +82.057 which is RA(J2000) = 16h 53m 06s Dec(J2000) = +82d 03' 26" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed two pulses with total duration of ~50 seconds. The first pulse happened at T0 lasting around 2 seconds, with peak count rate of ~3000 counts/sec (15-350 keV). The second pulse happened at ~T+45 with a duration of around 15 seconds and peak count rate ~2000 counts/sec (15-350 keV). The XRT began observing the field at 06:55:27.9 UT, 66.7 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source with an enhanced position: RA, Dec 253.2159, 82.0536 which is equivalent to: RA(J2000) = 16h 52m 51.83s Dec(J2000) = +82d 03' 13.0" with an uncertainty of 2.0 arcseconds (radius, 90% containment). This location is 31 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 (5.56 x 10^20 cm^-2, Kalberla et al. 2005), with an excess column of 2.6 (+1.37/-1.25) x 10^21 cm^-2 (90% confidence). The initial flux in the 2.5 s image was 9.38e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 869 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 19.6 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 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.08. Burst Advocate for this burst is B. N. Barlow (bbarlow AT highpoint.edu). 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.)