TITLE: GCN CIRCULAR NUMBER: 10834 SUBJECT: Trigger 424161: Swift/BAT trigger on XTE J1946+274/GRO J1944+26 DATE: 10/06/08 12:13:11 GMT FROM: David Burrows at PSU/Swift M. De Pasquale (UCL-MSSL), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), P. A. Curran (UCL-MSSL), V. D'Elia (ASDC), P. A. Evans (U Leicester), J. M. Gelbord (PSU), C. Guidorzi (U Ferrara), S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU), O. M. Littlejohns (U Leicester), V. Mangano (INAF-IASFPA), J. Mao (INAF-OAB), R. Margutti (INAF-OAB), S. R. Oates (UCL-MSSL), J. P. Osborne (U Leicester), C. Pagani (U Leicester), K. L. Page (U Leicester), P. Romano (INAF-IASFPA), A. Rowlinson (U Leicester), M. H. Siegel (PSU), M. Stamatikos (OSU/NASA/GSFC), R. L. C. Starling (U Leicester), T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU) report on behalf of the Swift Team: At 11:20:42 UT, the Swift Burst Alert Telescope (BAT) triggered on the cataloged source XTE J1946+274 (trigger=424161). Swift slewed to the source as soon as the BAT detected it as an image trigger. The BAT on-board calculated location is RA, Dec 296.430, +27.366 which is RA(J2000) = 19h 45m 43s Dec(J2000) = +27d 21' 57" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The XRT began observing the field at 11:51:28.2 UT, 1846.1 seconds after the BAT trigger. Using promptly downlinked data we find a bright X-ray source located at RA, Dec 296.41360, 27.36422 which is equivalent to: RA(J2000) = 19h 45m 39.26s Dec(J2000) = +27d 21' 51.2" with an uncertainty of 3.8 arcseconds (radius, 90% containment). This location is 53 arcseconds from the BAT onboard position, within the BAT error circle. This is 4.5 arcsec from the position of XTE J1946+274 (2MASS J19453935+2721555). The XRT position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (9.43e+21 cm^-2, Kalberla et al. 2005), with an excess column of 7.8 (+9.36/-7.22) x 10^21 cm^-2 (90% confidence). The initial flux in the 2.5 s image was 7.09e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 1854 seconds after the BAT trigger. No credible optical transient 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. No correction has been made for the large, but uncertain extinction expected.