TITLE: GCN CIRCULAR NUMBER: 13367 SUBJECT: Swift triggers (#524542) on a Galactic source DATE: 12/06/17 16:12:08 GMT FROM: Scott Barthelmy at NASA/GSFC S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU), V. D'Elia (ASDC), J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC), A. Maselli (INAF-IASFPA), D. M. Palmer (LANL) and G. Stratta (ASDC) report on behalf of the Swift Team: At 15:46:55 UT, the Swift Burst Alert Telescope (BAT) triggered and located a likely Galactic source (trigger=524542). Swift slewed immediately to the source. The BAT on-board calculated location is RA, Dec 282.785, +0.025 which is RA(J2000) = 18h 51m 08s Dec(J2000) = +00d 01' 29" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is typical for an image trigger (64 sec), the lightcurve does not show anything significant. The XRT began observing the field at 15:49:47.3 UT, 171.7 seconds after the BAT trigger. Using promptly downlinked data we find an X-ray source with an enhanced position: RA, Dec 282.8107, -0.0010 which is equivalent to: RA(J2000) = 18h 51m 14.57s Dec(J2000) = -00d 00' 03.6" with an uncertainty of 2.1 arcseconds (radius, 90% containment). This location is 131 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. This position is 3.0 arcseconds from that of a known X-ray source: 2XMM J185114.3-000004 in the XMM-NEWTON XMMSSC catalogue. The catalogued count-rate of this source is equivalent to approximately 0.013 XRT count/sec; the mean count-rate in the promptly-available XRT data is 0.56 count/sec. A power-law fit to a spectrum formed from promptly downlinked event data does not constrain the column density. UVOT took a finding chart exposure of 150 seconds with the White filter starting 175 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 none of the XRT error circle. The 8'x8' region for the list of sources generated on-board covers 100% of the BAT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the region. No correction has been made for the large, but uncertain extinction expected. Due to the extended duration of this detection and the proximity to the Galactic plane (0.04 degrees), we believe that this is most likely the Galactic source 2XMM J185114.3-000004 . However this is a crowded field and we cannot rule out the possibility that this is a different Galactic source.