TITLE: GCN CIRCULAR NUMBER: 11363 SUBJECT: GRB 101023A: Swift detection of a burst DATE: 10/10/23 23:32:06 GMT FROM: Jamie A. Kennea at PSU/Swift-XRT C. J. Saxton (UCL-MSSL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester), M. M. Chester (PSU), J. R. Cummings (NASA/UMBC), M. De Pasquale (UCL-MSSL), N. Gehrels (NASA/GSFC), J. M. Gelbord (PSU), S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU), O. M. Littlejohns (U Leicester), C. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC), S. R. Oates (UCL-MSSL), K. L. Page (U Leicester), D. M. Palmer (LANL), M. Stamatikos (OSU/NASA/GSFC), R. L. C. Starling (U Leicester) and E. Troja (NASA/GSFC/ORAU) report on behalf of the Swift Team: At 22:50:12 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 101023A (trigger=436981). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 317.954, -65.394 which is RA(J2000) = 21h 11m 49s Dec(J2000) = -65d 23' 37" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The lightcurve shows a small initial pulse at T+0 seconds with a large FRED pulse at about T+55 sec. The peak flux was 32000 counts/sec at T+55 sec. The XRT began observing the field at 22:51:36.9 UT, 84.5 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 317.9704, -65.3859 which is equivalent to: RA(J2000) = 21h 11m 52.89s Dec(J2000) = -65d 23' 09.2" with an uncertainty of 5.3 arcseconds (radius, 90% containment). This location is 37 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. UVOT took a finding chart exposure of 100 seconds with the White filter starting 92 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 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. The XRT position lies 10.6" from a catalogued USNO object, photometry is difficult due to the bright halo of the 13th magnitude USNO star. More data is required to determine if a new source is present. Burst Advocate for this burst is C. J. Saxton (cjs2@mssl.ucl.ac.uk). 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.)