TITLE: GCN CIRCULAR NUMBER: 34981 SUBJECT: GRB 231111A: Swift detection of a burst with an optical counterpart DATE: 23/11/11 14:33:33 GMT FROM: Jamie Kennea at Penn State A. Melandri (INAF-OAR), E. Ambrosi (INAF-IASFPA), A. D'Ai (INAF-IASFPA), S. Dichiara (PSU), J.D. Gropp (PSU), J. A. Kennea (PSU) and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team: At 14:17:19 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 231111A (trigger=1195887). Swift slewed immediately to the event. The BAT on-board calculated location is RA, Dec 290.234, +52.447 which is RA(J2000) = 19h 20m 56s Dec(J2000) = +52d 26' 49" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Due to a telemetry outage, there is no immediately available BAT lightcurve information. However the trigger information indicates an initial count rate of 3100 counts/s (25-100 keV) on a 1 second timescale. The XRT began observing the field at 14:18:59.3 UT, 99.6 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 290.1915, 52.4383 which is equivalent to: RA(J2000) = 19h 20m 45.96s Dec(J2000) = +52d 26' 17.9" with an uncertainty of 5.5 arcseconds (radius, 90% containment). This location is 98 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 238 seconds with the U filter starting 164 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 19:20:45.24 = 290.18848 DEC(J2000) = +52:26:10.5 = 52.43626 with a 90%-confidence error radius of about 0.62 arc sec. This position is 9.9 arc sec. from the center of the XRT error circle. The estimated magnitude is 16.51 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.117. Burst Advocate for this burst is A. Melandri (andrea.melandri AT inaf.it). 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/)