TITLE: GCN CIRCULAR NUMBER: 8000 SUBJECT: GRB 080723: Swift detection of a burst DATE: 08/07/23 04:40:07 GMT FROM: David Palmer at LANL M. Stamatikos (NASA/ORAU), W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester), S. T. Holland (CRESST/USRA/GSFC), S. D. Hunsberger (PSU), H. A. Krimm (CRESST/GSFC/USRA), C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL) and T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team: At 04:19:24 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 080723 (trigger=317662). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 274.512, -6.923 which is RA(J2000) = 18h 18m 03s Dec(J2000) = -06d 55' 20" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Because the BAT light curve has not been received, we cannot comment on the burst profile at this time. However, there is a strong 8.4 sigma excess detected in the scaled map image, which strongly suggests a real gamma-ray burst occurred. The XRT began observing the field at 04:20:50.2 UT, 85.8 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 274.48985, -6.89931 which is equivalent to: RA(J2000) = 18h 17m 57.56s Dec(J2000) = -06d 53' 57.5" with an uncertainty of 2.7 arcseconds (radius, 90% containment). This location is 116 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 in excess of the Galactic value (3.94e+21 cm^-2, Kalberla et al. 2005), with an excess column of 5.7 (+6.36/-4.59) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 92 seconds after the BAT trigger. No afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 0% of the XRT error circle. 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 large Galactic expected extinction corresponding to E(B-V) of 1.3 mag. Burst Advocate for this burst is M. Stamatikos (michael AT milkyway.gsfc.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.)