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GCN Circular 21095

Subject
Swift Trigger on AXP CXOU J164710.2-455216
Date
2017-05-16T07:44:47Z (8 years ago)
From
Kim Page at U.of Leicester <klp5@leicester.ac.uk>
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 5581Loading...
 
  and 12359Loading...
 
 ). 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.