TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5583 SUBJECT: GRB 060923: Swift detection of a burst DATE: 06/09/23 05:41:32 GMT FROM: David Burrows at PSU/Swift M. Stamatikos (NASA/ORAU), D. N. Burrows (PSU), M. Capalbi (ASDC), M.L. Conciatore (ASDC), N. Gehrels (NASA/GSFC), C. Guidorzi (Univ Bicocca&INAF-OAB), S. T. Holland (GSFC/USRA), D. M. Palmer (LANL), M. Perri (ASDC), T. Sakamoto (NASA/ORAU) and D. E. Vanden Berk (PSU) report on behalf of the Swift Team: At 05:12:15 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 060923 (trigger=230662). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 254.623, +12.379 {16h 58m 30s, +12d 22' 45"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed at least two peaks, lasting 12 seconds. The peak count rate was ~1200 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began taking data at 05:13:36 UT, 81 seconds after the BAT trigger. The XRT found a previously uncatalogued X-ray source in the field of view at the following coordinates: RA(J2000) = 16 58 28.27 Dec(J2000)= +12 21 43.3 with an uncertainty of 6.9 arcseconds radius (90% containment). This position lies 67 arcseconds from the center of the BAT error circle. The approximate initial flux is 1.7e-11 erg/cm2/sec (0.2-10 keV). UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 85 seconds after the BAT trigger. No afterglow candidate has been found in the initial data products. The overlap of the sub-image and the XRT error circle is 100%. The overlap of the 8'x8' region for the list of sources generated on-board and the XRT error circle is 100%. The limiting magnitude of the finding chart image is approximately 18.5. No correction has been made for the expected extinction corresponding to E(B-V) of 0.06.