TITLE: GCN CIRCULAR NUMBER: 5760 SUBJECT: GRB 061027: Swift detection of a possible burst DATE: 06/10/27 10:48:55 GMT FROM: Scott Barthelmy at NASA/GSFC M. Stamatikos (NASA/ORAU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), S. Campana (INAF-OAB), M. M. Chester (PSU), G. Cusumano (INAF-IASFPA), N. Gehrels (NASA/GSFC), C. Guidorzi (Univ Bicocca&INAF-OAB), K. M. McLean (LANL/UTD), T. Mineo (INAF-IASFPA), P. T. O'Brien (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), S. B. Pandey (UCL-MSSL), P. Romano (Univ. Bicocca & INAF-OAB) and T. Sakamoto (NASA/ORAU) report on behalf of the Swift Team: At 10:15:02 UT, the Swift Burst Alert Telescope (BAT) triggered and located possible GRB 061027 (trigger=235645). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 270.812, -82.228 {18h 03m 15s, -82d 13' 39"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). This is a 64-sec image trigger and as is typical the BAT lightcurve does not show any significant emission. The image peak is barely above the significance threshold for automatic detection, and therefore this may be a statistical fluctuation. The XRT began taking data at 10:17:29 UT, 147 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. Initial down-linked data products also show no evidence for any X-ray source in the image in ~200 s of data. This gives a very rough upper limit of 2E-12 erg/cm2/s for any source in the field of view. We note that only one long burst has had no XRT detection following a prompt slew, out of 119 long GRBs observed by XRT with prompt slews to date. Further analysis awaits the full dowloaded data products. UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 151.7 seconds after the BAT trigger. No afterglow candidate has been found in the initial data products. The limiting magnitude of the finding chart image is approximately 19.0. No correction has been made for the expected extinction.