TITLE: GCN CIRCULAR NUMBER: 6706 SUBJECT: Swift detection of a outburst from SAX J1810.8-2609 DATE: 07/08/05 12:11:10 GMT FROM: Scott Barthelmy at NASA/GSFC A. M. Parsons (GSFC), S. D. Barthelmy (GSFC), N. Gehrels (NASA/GSFC), C. Guidorzi (Univ Bicocca&INAF-OAB), H. A. Krimm (GSFC/USRA), V. La Parola (INAF-IASFPA), V. Mangano (INAF-IASFPA), C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), P. Romano (Univ. Bicocca & INAF-OAB), G. Sato (GSFC/ISAS), B. Sbarufatti (INAF-IASFPA), R. L. C. Starling (U Leicester), E. Troja (INAF-IASFPA), D. E. Vanden Berk (PSU) and H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team: At 2007-08-05 11:27:26 UT, the Swift Burst Alert Telescope (BAT) triggered on a burst source not in its onboard catalog (trigger=287042). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec = 272.651, -26.153 which is RA(J2000) = 18h 10m 36s Dec(J2000) = -26d 09' 10" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). This source location is consistent (1.8 arcmin) with the known Low Mass X-ray Binary V* V4722 Sgr (=SAX J1810.8-2609). The BAT light curve shows a single peak with a duration of roughly 5 sec. The peak count rate was ~600 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 11:28:25 UT, 59 seconds after the BAT trigger. XRT found a bright, variable X-ray source whose position, determined from downlinked data, is RA, Dec 272.68594, -26.15055 which is RA(J2000) = 18h 10m 44.63s Dec(J2000) = -26d 09' 02.0" with an uncertainty of 4.5 arcseconds (radius, 90% containment). This location is 112 arcseconds from the BAT on-board position, within the BAT error circle. The initial flux in the 2.5s image was 4.9e-09 erg/cm2/s (0.2-10 keV). The position is 3.69 arcseconds from the LMXB V* V4722 Sgr. UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 70 seconds after the BAT trigger. No afterglow candidate has been found in the initial data products. There is a high density of sources in the image. The extinction toward the field is high, with E(B-V)=0.95. Burst Advocate for this burst is A. M. Parsons (parsons 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.)