GCN Circular 22389

S. D. Barthelmy (GSFC), A. Deich (PSU), J.D. Gropp (PSU),
J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
B. Sbarufatti (PSU) and A. Tohuvavohu (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 19:27:11 UT, the Swift Burst Alert Telescope (BAT) triggered and
located on CXOU J164710.2-455216/PSR J1647-4552 (trigger=808755).  
Swift slewed immediately to the source. 
The BAT on-board calculated location is 
RA, Dec 251.749, -45.850 which is 
   RA(J2000) = 16h 47m 00s
   Dec(J2000) = -45d 51' 00"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
structure with a duration of about 0.4 sec.  The peak count rate
was ~4000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 19:27:50.6 UT, 38.9 seconds after
the BAT trigger. Using promptly downlinked data we find an X-ray source
with an enhanced position: RA, Dec 251.7918, -45.8713 which is
equivalent to:
   RA(J2000)  = 16h 47m 10.17s
   Dec(J2000) = -45d 52' 16.2"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 132 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 1.6 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
Not found
 
 
, 12359
Not found
 
 
, 21095
Not found
 
 
, 22024
Not found
 
 
 and 22025
Not found
 
 
). This source 
is 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 2.2
(+2.52/-1.78) x 10^22 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 250 seconds with the U filter 
starting 99  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 typical upper limit has been about 18th mag. No correction  has
been made for the large, but uncertain,  extinction expected.