TITLE: GCN CIRCULAR NUMBER: 17416 SUBJECT: Trigger 630047: Swift detection of 1RXS J180408.9-342058 DATE: 15/02/06 21:26:24 GMT FROM: Scott Barthelmy at NASA/GSFC S. D. Barthelmy (GSFC), D. N. Burrows (PSU), C. Gronwall (PSU), M.E. Gropp (PSU), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), D. Malesani (DARK/NBI), F. E. Marshall (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 20:45:14 UT, the Swift Burst Alert Telescope (BAT) triggered and located 1RXS J180408.9-342058 (trigger=630047). Swift slewed to the source. The BAT on-board calculated location is RA, Dec 271.019, -34.318, which is RA(J2000) = 18h 04m 05s Dec(J2000) = -34d 19' 03" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is typical for image triggers (15 min integration), there is nothing discernible from the real-time data. The XRT began observing the field at 21:04:28.5 UT, 1153.7 seconds after the BAT trigger. XRT found a bright X-ray source located at RA, Dec 271.0338, -34.3481 which is equivalent to: RA(J2000) = +18h 04m 8.11s Dec(J2000) = -34d 20' 53.2" with an uncertainty of 5.3 arcseconds (radius, 90% containment). This location is 116 arcseconds from the BAT onboard position, within the BAT error circle. This position is 4.8 arcseconds from a known X-ray source: 1SXPS J180408.1-342048. This source is in the Swift XRT 1SXPS catalogue with a mean 0.3-10 keV count-rate of 0.0256 +/- 0.0020 ct/sec; see http://www.swift.ac.uk/1SXPS/1SXPSJ180408.1-342048 for details of these previous observations. 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 1.37e-09 erg cm^-2 s^-1 (0.2-10 keV), corresponding to ~30 counts per second. UVOT took a finding chart exposure of 150 seconds with the White filter starting 1163 seconds after the BAT trigger. There is an optical counterpart in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 18:04:08.40 = 271.03499 DEC(J2000) = -34:20:51.2 = -34.34755 with a 90%-confidence error radius of about 0.62 arc sec. This position is 4.0 arc sec. from the center of the XRT error circle. The estimated magnitude is 17.29 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.48. This is the second BAT trigger on 1RXS J180408.9-342058. The first was on January 31st, 2015 at 21:14UT (GCN #17367). The recent rise in brightness of this object has been reported by the BAT Transient Monitor (ATEL #6997) and MAXI (ATEL #7008).