TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5590 SUBJECT: GRB 060923B: Swift detection of a burst DATE: 06/09/23 12:02:46 GMT FROM: Scott Barthelmy at NASA/GSFC M. Stamatikos (NASA/ORAU), S. D. Barthelmy (GSFC), 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), J. A. Kennea (PSU), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), M. Perri (ASDC), T. Sakamoto (NASA/ORAU), D. E. Vanden Berk (PSU) and H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team: At 11:38:06 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 060923B (trigger=230702). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 238.201, -30.907 {15h 52m 48s, -30d 54' 25"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a single peak with a duration of about 10 sec. The peak count rate was ~1500 counts/sec (15-350 keV), at ~4 sec after the trigger. The XRT began observing the field at 11:40:00 UT, 114 seconds after the BAT trigger. XRT centroided on a cosmic ray on-board, so the position sent out in our first, automated XRT Position Notice is incorrect. From preliminary ground analysis of photon-counting mode data, XRT did find an uncatalogued X-ray source located at RA(J2000) = 15h 52m 46.83s, Dec(J2000) = -30d 54' 12.6", with an estimated uncertainty of 6.5 arcseconds (90% confidence radius). This position was sent out via BACODINE in a second XRT Position Notice with the correct position. This location is 21 arcseconds from the BAT on-board position, within the BAT error circle. The initial flux in the 2.5s image was 2.4e-11 erg/cm2/s (0.2-10 keV). UVOT took a finding chart exposure of nominal 200 seconds with the White (160-650 nm) filter starting 122 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. The overlap of the sub-image and the XRT error circle is 100%. No source is seen in the XRT error circle to a magnitude of approximately 18.5. No correction has been made for the expected extinction corresponding to E(B-V) of 0.15.