TITLE: GCN CIRCULAR NUMBER: 7665 SUBJECT: GRB 080503: Swift detection of a short burst DATE: 08/05/03 12:50:13 GMT FROM: David Burrows at PSU/Swift J. Mao (INAF-OAB), W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU), M. M. Chester (PSU), N. Gehrels (NASA/GSFC), C. Guidorzi (INAF-OAB), S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU), C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester), D. M. Palmer (LANL), P. Romano (INAF-IASFPA), T. N. Ukwatta (GSFC/GWU) and D. E. Vanden Berk (PSU) report on behalf of the Swift Team: At 12:26:13 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 080503 (trigger=310785). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 286.617, +68.778 which is RA(J2000) = 19h 06m 28s Dec(J2000) = +68d 46' 41" 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 0.5 sec, although there may be further activity during the slew. The peak count rate was ~6500 counts/sec (15-350 keV), at ~0.1 sec after the trigger. The XRT began observing the field at 12:27:28.1 UT, 74.9 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source with an enhanced position: RA, Dec 286.62049, 68.79379 which is equivalent to: RA(J2000) = 19h 06m 28.92s Dec(J2000) = +68d 47' 37.6" with an uncertainty of 2.7 arcseconds (radius, 90% containment). This location is 57 arcseconds from the BAT onboard position, within the BAT error circle. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 5.56e+20 cm^-2 (Kalberla et al. 2005), so we cannot constrain the redshift at this time using the relation from Grupe et al. (2007). A summary of the promptly downlinked data is given at http://www.swift.ac.uk/sper/310785/. The initial flux in the 2.5 s image was 7.82e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 84 seconds after the BAT trigger. No 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 3-sigma upper limit is about 20th 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 0.06. Burst Advocate for this burst is J. Mao (jirong.mao 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.)