TITLE: GCN CIRCULAR NUMBER: 23342 SUBJECT: GRB 181016A: Swift detection of a burst DATE: 18/10/16 01:07:47 GMT FROM: David Palmer at LANL P. D'Avanzo (INAF-OAB), H. A. Krimm (NSF/USRA), D. M. Palmer (LANL), T. Sakamoto (AGU), B. Sbarufatti (PSU) and A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 00:55:00 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 181016A (trigger=867252). Due to an observing constraint, Swift could not slew to the burst. The BAT on-board calculated location is RA, Dec 231.268, -35.279 which is RA(J2000) = 15h 25m 04s Dec(J2000) = -35d 16' 43" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 40 sec. The peak count rate was ~500 counts/sec (15-350 keV), at ~0 sec after the trigger. Due to a Sun observing constraint, Swift cannot slew to the BAT position until 09:03 UT on 2019 January 03. There will thus be no XRT or UVOT data for this trigger before this time. Burst Advocate for this burst is P. D'Avanzo (paolo.davanzo AT brera.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/too.html.)