TITLE: GCN CIRCULAR NUMBER: 13774 SUBJECT: Swift Trigger 533836 is a new Galactic transient DATE: 12/09/16 10:05:16 GMT FROM: David Palmer at LANL J. R. Cummings (NASA/UMBC), C. Gronwall (PSU), D. Grupe (PSU), H. A. Krimm (CRESST/GSFC/USRA), C. B. Markwardt (NASA/GSFC), D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU) and M. Stamatikos (OSU/NASA/GSFC) report on behalf of the Swift Team: At 09:16:06 UT, the Swift Burst Alert Telescope (BAT) triggered and located an unidentified source near the Galactic center (trigger=533836). Swift slewed immediately to the source location. The BAT on-board calculated location is RA, Dec 266.322, -26.400 which is RA(J2000) = 17h 45m 17s Dec(J2000) = -26d 23' 58" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). This is a 16 minute long image trigger, so there is no immediately available lightcurve data. The on-board detection significance is 8.5 sigma. The XRT began observing the field at 09:36:59.0 UT, 1252.7 seconds after the BAT trigger. XRT found a possible X-ray source located at RA, Dec 266.2960, -26.4025 which is equivalent to: RA(J2000) = +17h 45m 11.04s Dec(J2000) = -26d 24' 09.0" with an uncertainty of 5.8 arcseconds (radius, 90% containment). This location is 84 arcseconds from the BAT onboard position, within the BAT error circle. We are waiting for the full dataset to download in order to confirm the existence of the source. The initial flux in the 2.5 s image was 8.01e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 1259 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. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the sub-image. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT 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 its position 152 arcminutes from the Galactic center, and its duration (discovered in a 16-minute long imag trigger), we believe that this is a previously-uncatalogued Galactic transient. A final determination of the status of this source will require the downlinked data from the ground station. A 'Swift J' source name will be assigned based on the final X-ray position.