TITLE: GCN CIRCULAR NUMBER: 8421 SUBJECT: GRB 081028: Swift detection of a burst DATE: 08/10/28 00:44:50 GMT FROM: David Palmer at LANL C. Guidorzi (INAF-OAB), W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester), J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC), S. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL), T. Sakamoto (NASA/UMBC), M. Stamatikos (NASA/ORAU) and T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team: At 00:25:00 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 081028 (trigger=332851). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 121.890, +2.311 which is RA(J2000) = 08h 07m 34s Dec(J2000) = +02d 18' 40" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Although this is a BAT image trigger, the BAT light curve showed at least two slowly rising and falling peak structure with a duration of about 250 sec. The peak count rate of the first peak was ~600 counts/sec (15-350 keV), at ~70 sec after the trigger. The second peak was comparable in size peaking at ~210 sec. The XRT began observing the field at 00:28:11.5 UT, 190.7 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 121.8953, +2.3086 which is equivalent to: RA(J2000) = 08h 07m 34.87s Dec(J2000) = +02d 18' 30.9" with an uncertainty of 4.8 arcseconds (radius, 90% containment). This location is 20 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 2.5 s image was 5.50e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of nominal 150 seconds with the White (160-650 nm) filter starting 200 seconds after the BAT trigger. No afterglow candidate has been found in the initial data products. Image catalog data are not available at this time. 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 0.03. Burst Advocate for this burst is C. Guidorzi (cristiano.guidorzi 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.)