TITLE: GCN CIRCULAR NUMBER: 14911 SUBJECT: Trigger 558399: Swift detection of the Soft Gamma Repeater AXP 1E1547.0-5408 DATE: 13/06/17 10:28:00 GMT FROM: David Palmer at LANL S. T. Holland (STScI), A. Y. Lien (NASA/GSFC/ORAU), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), T. Sakamoto (AGU) and B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team: At 09:52:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located a burst from the Soft Gamma Repeater AXP 1E1547.0-5408 (trigger=558399). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 237.714, -54.277 which is RA(J2000) = 15h 50m 51s Dec(J2000) = -54d 16' 35" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single spike structure with a duration of about 0.2 sec. The peak count rate was ~8570 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 09:53:41.8 UT, 71.8 seconds after the BAT trigger. Using promptly downlinked data we find an X-ray source with an enhanced position: RA, Dec 237.7266, -54.3063 which is equivalent to: RA(J2000) = 15h 50m 54.39s Dec(J2000) = -54d 18' 22.6" with an uncertainty of 2.7 arcseconds (radius, 90% containment). This location is 108 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. This position is 1.8 arcseconds from that of AXP 1E1547.0-5408. A power-law fit to a spectrum formed from promptly downlinked event data does not constrain the column density. UVOT took a finding chart exposure of 150 seconds with the White filter starting 75 seconds after the BAT trigger. No credible counterpart has been found in the initial data products. The 2.7'x2.7' sub-image covers none of the XRT error circle. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the large, but uncertain extinction expected. This soft gamma repeater had a major period of activity in October, 2008 (ATEL #1756, Rea et al., 2008) and was last seen by Swift BAT on 2011-12-20.