TITLE: GCN CIRCULAR NUMBER: 19514 SUBJECT: Trigger 689956: Swift detection of a source near the Galactic center DATE: 16/06/09 03:15:50 GMT FROM: Scott Barthelmy at NASA/GSFC S. D. Barthelmy (GSFC), D. M. Palmer (LANL), T. G. R. Roegiers (PSU) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 02:21:03 UT, the Swift Burst Alert Telescope (BAT) triggered and located a possible new source (trigger=689956). Swift did not immediately slew to the source due to its low merit value. The BAT on-board calculated location is RA, Dec 266.422, -29.008, which is RA(J2000) = 17h 45m 41s Dec(J2000) = -29d 00' 29" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is typical for image triggers (especially long triggers such as this 15 min one), the real-time TDRSS data does not show anything significant. The XRT began observing the field at 02:56:14.5 UT, 2110.9 seconds after the BAT trigger. Using promptly downlinked data we find an X-ray source located at RA, Dec 266.41879, -29.01122 which is equivalent to: RA(J2000) = 17h 45m 40.51s Dec(J2000) = -29d 00' 40.4" with an uncertainty of 3.7 arcseconds (radius, 90% containment). 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 2.2 arcseconds from that of a known X-ray source: 1BMC 174540.6-290039 in the CHANDRA BMWCHANCAT catalogue 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 2113 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 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the large, but uncertain extinction expected. This source is presumably the same as the source that triggered 2.5 days earlier (Barthelmy et al. GCN 19499). This may be the recently-detected source SWIFT J174540.2-290037 which has continued to brighten in the XRT during routine monitoring (Degenaar et al. Atel #9109), the previously detected and currently- active SWIFT J174540.7-290015 (Reynolds et al; ATel #8649) or some other source such as 1BMC 174540.6-290039, located by XRT in the initial exposure. Due to the crowded field this close to the Galactic center (~4 arcminutes) we cannot definitively determine which source produced either trigger with the currently-available data.