TITLE: GCN CIRCULAR NUMBER: 21095 SUBJECT: Swift Trigger on AXP CXOU J164710.2-455216 DATE: 17/05/16 07:44:47 GMT FROM: Kim Page at U.of Leicester A. D'Ai (INAF-IASFPA), P.A. Evans (U Leicester), H. A. Krimm (NSF/USRA), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (GSFC/UMBC) and K. L. Page (U Leicester) report on behalf of the Swift Team: At 07:09:02 UT, the Swift Burst Alert Telescope (BAT) triggered and located an outburst (trigger=753085). Swift slewed immediately to the location. The BAT on-board calculated location is RA, Dec 251.827, -45.895 which is RA(J2000) = 16h 47m 18s Dec(J2000) = -45d 53' 40" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single short spike with a duration of about 0.1 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 07:09:57.4 UT, 55.5 seconds after the BAT trigger. Using promptly downlinked data we find an X-ray source with an enhanced position: RA, Dec 251.7913, -45.8715 which is equivalent to: RA(J2000) = 16h 47m 09.91s Dec(J2000) = -45d 52' 17.5" with an uncertainty of 2.7 arcseconds (radius, 90% containment). This location is 122 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. We cannot determine whether the source is fading at the present time. This position is 2.9 arcseconds from a known X-ray source: CXOU J164710.2-455216/PSR J1647-4552, a known magnetar (e.g. Woods et al., 2011, ApJ, 726, 37), which has triggered BAT previously (GCNs 5581 and 12359). This source is also in the Swift XRT 1SXPS catalogue with a mean 0.3-10 keV count-rate of 0.2290 +/- 0.0028 ct/sec; see http://www.swift.ac.uk/1SXPS/1SXPSJ164710.3-455217 for details of these previous observations. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (2.03 x 10^22 cm^-2, Willingale et al. 2013), with an excess column of 3.8 (+4.22/-3.09) x 10^22 cm^-2 (90% confidence). UVOT observed the source in the U band and the resulting source list was examined. No source was detected at the XRT position. The E(B-V) = 11 and its high value is consistent with no detection in the UVOT.