TITLE: GCN CIRCULAR NUMBER: 23389 SUBJECT: GRB 181030A: Swift detection of a burst with a possible optical counterpart DATE: 18/10/30 01:50:20 GMT FROM: David Palmer at LANL E. Sonbas (Adiyaman Univ.), J.D. Gropp (PSU), J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC), M. J. Moss (George Washington University), K. L. Page (U Leicester), M. H. Siegel (PSU) and A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 01:27:22 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 181030A (trigger=869494). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 146.922, +14.658 which is RA(J2000) = 09h 47m 41s Dec(J2000) = +14d 39' 28" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is usual with an image trigger, the available BAT light curve shows no significant structure. The XRT began observing the field at 01:29:44.2 UT, 142.1 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 146.9251, 14.6582 which is equivalent to: RA(J2000) = 09h 47m 42.02s Dec(J2000) = +14d 39' 29.5" with an uncertainty of 4.8 arcseconds (radius, 90% containment). This location is 10 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. The initial flux in the 2.5 s image was 5.25e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 118 seconds with the White filter starting 151 seconds after the BAT trigger. There is a possible afterglow in the rapidly available 2.7'x2.7' sub-image near the position of the XRT afterglow. A precise position is unavailable due to a failed aspect correction. The estimated magnitude is 18.94 with a 1-sigma error of about 0.22. Burst Advocate for this burst is E. Sonbas (edasonbas AT yahoo.com). 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.)