TITLE: GCN CIRCULAR NUMBER: 16594 SUBJECT: Swift detection of UX Ari DATE: 14/07/15 21:42:34 GMT FROM: David Palmer at LANL W. H. Baumgartner (GSFC/UMBC), L. M. Z. Hagen (PSU), H. A. Krimm (CRESST/GSFC/USRA), A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), C. J. Mountford (U Leicester), C. Pagani (U Leicester) and K. L. Page (U Leicester) report on behalf of the Swift Team: At 21:14:11 UT, the Swift Burst Alert Telescope (BAT) triggered and located the RS CVn star UX Ari (trigger=604675). Swift slewed immediately to the source. The BAT on-board calculated location is RA, Dec 51.649, +28.717 which is RA(J2000) = 03h 26m 36s Dec(J2000) = +28d 43' 01" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is usual for image triggers, there is no obvious variation in the light curve. Because BAT triggered on the first 5-minute image of a pointing, it is likely that the source was already in outburst at the nominal trigger time. The XRT began observing the field at 21:20:38.6 UT, 386.9 seconds after the BAT trigger. XRT found a bright X-ray source located at RA, Dec 51.6474, 28.7144 which is equivalent to: RA(J2000) = +03h 26m 35.38s Dec(J2000) = +28d 42' 51.8" with an uncertainty of 4.8 arcseconds (radius, 90% containment). This location is 10 arcseconds from the BAT onboard position, within the BAT error circle. This position is consistent with UX Ari, also designated as 3XMM J032635.3+284254 in the XMM-NEWTON XMMSSC catalogue. 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 7.65e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the U filter starting 862 seconds after the BAT trigger. UVOT detects a very bright source consistent with the position of UX Ari. Because of dead time effects, more analysis is required to estimate a position or the magnitude.