TITLE:   GCN CIRCULAR
NUMBER:  22027
SUBJECT: Fermi-GBM Detection of possible burst from AXP CXOU J164710.2-455216/PSR J1647-4552
DATE:    17/10/19 18:51:45 GMT
FROM:    Oliver J Roberts at USRA/NASA  <oliver.roberts@nasa.gov>

O.J. Roberts (USRA), R. Hamburg (UAH), M.S. Briggs (UAH), 
V. Connaughton (USRA), C. Kouveliotou (GWU) and G. Younes (GWU) 
report on behalf of the Fermi-GBM Team:

"At 01:01:16.25 UT on 19 October 2017, the Fermi Gamma-Ray 
Burst Monitor triggered (trigger 530067681 / 171019043) 
on a bright SGR-like burst. The GBM on-ground location is 
consistent with the position of the known source 
AXP CXOU J164710.2-455216/PSR J1647-4552, which later 
triggered Swift-BAT (Beardmore et al., GCN 22024 and 
Lien et al., GCN 22025). MAXI also triggered on a 
transient from a position consistent with the source.

The GBM light curve shows two bright, short peaks each with
a duration (T90) of about 0.1 s. The time-averaged spectrum
over both peaks from T0-0.064 to T0+0.384 is best fit by a 
power-law function with an exponential high-energy cutoff.  
The power law index is 0.04 +/- 0.13 and the cutoff energy, 
parameterized as Epeak, is 35 +/- 1 keV.

The event fluence (10-1000 keV) in this time interval is
(7.4 +/- 0.12)E-07 erg/cm^2. The photon flux measured starting
from T0-0.64 s in the 10-1000 keV band is 37 +/- 1 ph/s/cm^2.

An offline search of the GBM time-tagged event data optimized
to find sub-threshold short GRBs uncovered at least one
additional burst that could have come from this source.  
This is consistent with the ongoing source activity reported
by Lien et al. (GCN 22025). The offline search results are
distributed as GCN notices 
(https://gcn.gsfc.nasa.gov/admin/fermi_gbm_subthreshold_announce.txt)
with the notice archive available at 
https://gcn.gsfc.nasa.gov/fermi_gbm_subthresh_archive.html.
The results of a dedicated search for magnetar bursts will be 
presented in a future circular."