TITLE: GCN CIRCULAR NUMBER: 23413 SUBJECT: GRB 181110A: Swift detection of a burst with an optical counterpart DATE: 18/11/10 08:59:09 GMT FROM: Kim Page at U.of Leicester P. A. Evans (U Leicester), K. L. Page (U Leicester) and T. Sakamoto (AGU) report on behalf of the Neil Gehrels Swift Observatory Team: At 08:43:31 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 181110A (trigger=871316). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 302.342, -36.903 which is RA(J2000) = 20h 09m 22s Dec(J2000) = -36d 54' 08" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi-peaked structure with a duration of about 150 sec. The peak count rate was ~3870 counts/sec (15-350 keV), at ~10 sec after the trigger. The XRT began observing the field at 08:44:35.2 UT, 64.0 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 302.31711, -36.89632 which is equivalent to: RA(J2000) = 20h 09m 16.11s Dec(J2000) = -36d 53' 46.8" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 75 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. We cannot determine whether the source is fading at the present time. No spectrum from the promptly downlinked event data is yet available to determine the column density. The initial flux in the 0.1 s image was 5.82e-08 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 72 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 20:09:16.28 = 302.31782 DEC(J2000) = -36:53:47.8 = -36.89661 with a 90%-confidence error radius of about 0.63 arc sec. This position is 3.3 arc sec. from the center of the XRT error circle. The estimated magnitude is 18.39 with a 1-sigma error of about 0.15. No correction has been made for the expected extinction corresponding to E(B-V) of 0.07. Burst Advocate for this burst is P. A. Evans (pae9 AT star.le.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.)