TITLE: GCN CIRCULAR NUMBER: 5480 SUBJECT: GRB 060826(?): Swift detection of a possible burst DATE: 06/08/26 10:36:35 GMT FROM: Scott Barthelmy at NASA/GSFC M. Stamatikos (NASA/ORAU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), M. M. Chester (PSU), N. Gehrels (NASA/GSFC), C. Guidorzi (Univ Bicocca&INAF-OAB), S. T. Holland (GSFC/USRA), K. L. Page (U Leicester), D. M. Palmer (LANL), A. M. Parsons (GSFC), M. C. Stroh (PSU) and H. Z. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team: At 09:58:14 UT, the Swift Burst Alert Telescope (BAT) triggered and located a possible GRB 060826 (trigger=226614). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 208.219, +11.871 {13h 52m 53s, +11d 52' 16"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The lightcurve shows little structure, which is typical for image triggers. Given the little information received to date on this trigger, we can not rule out a non-astrophysical cause for this trigger. The XRT began taking data at 10:00:20 UT, 126 seconds after the BAT trigger. The XRT on-board centroid algorithm did not find a source in the image and no prompt position is available. In 285 seconds of downlinked data, we find no concentration of photons at all. We note that the non-detection of a long burst by the XRT after a prompt slew is extremely unusual. We are waiting for more complete down-linked data to perform a more sensitive search for a faint source in the BAT error circle. UVOT took a finding chart exposure of 100 seconds with the uvm2 (166-268 nm) filter starting 123.7 seconds after the BAT trigger. No images in optical filters were taken due to a bright star in the field of view. No afterglow candidate has been found in the initial data products. The 8'x8' region for the list of sources generated on-board covers 25% 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 0.026.