TITLE: GCN CIRCULAR NUMBER: 14735 SUBJECT: GRB 130603B: Swift detection of a bright short burst DATE: 13/06/03 16:15:25 GMT FROM: David Palmer at LANL A. Melandri (INAF-OAB), W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU), J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC), C. Gronwall (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL), R. L. C. Starling (U Leicester) and T. N. Ukwatta (MSU) report on behalf of the Swift Team: At 15:49:14 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 130603B (trigger=557310). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 172.209, +17.045 which is RA(J2000) = 11h 28m 50s Dec(J2000) = +17d 02' 42" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single spike structure with a duration of about 0.4 sec. The peak count rate was 60000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 15:50:12.8 UT, 59.0 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 172.2006, 17.0719 which is equivalent to: RA(J2000) = 11h 28m 48.16s Dec(J2000) = +17d 04' 18.8" with an uncertainty of 2.7 arcseconds (radius, 90% containment). This location is 101 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 (1.93 x 10^20 cm^-2, Kalberla et al. 2005), with an excess column of 6.8 (+4.00/-3.31) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 62 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. 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 BAT 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 0.02. The Swift star trackers were not locked at the time of the burst, so there may be some additional error in the position. However the spike in the rates and the image detection is unambiguously real. We note that this bright short hard GRB is near (12 arcminutes) the location of the nearby galaxy NGC 3691. At z=0.003566, this corresponds to a nominal projected distance of about 50 kpc. 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.)