[vsnet-grb-info 25284] SGR Swift J1818.0-1607: Swift-BAT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  27384
SUBJECT: SGR Swift J1818.0-1607: Swift-BAT refined analysis
DATE:    20/03/14 05:40:49 GMT
FROM:    Takanori Sakamoto at AGU  <tsakamoto at phys.aoyama.ac.jp>

M. Stamatikos (OSU), S. D. Barthelmy (GSFC), J. R. Cummings (CPI),
P. A. Evans (U Leicester), H. A. Krimm (NSF),S. Laha (GSFC/UMBC),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):
  
Using the data set from T-61 to T+242 sec from the recent telemetry downlink,
we report further analysis of the BAT detection of a burst from a newly
discovered SGR Swift J1818.0-1607 (trigger #960986)
(Evans, et al., GCN Circ. 27373).  The BAT ground-calculated position is
RA, Dec = 274.515, -16.125 deg which is
    RA(J2000)  =  18h 18m 03.7s
    Dec(J2000) = -16d 07' 31.8"
with an uncertainty of 2.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 99%.
  
The mask-weighted light curve in 2 ms time bins shows a burst that starts
at T-0.005 sec, peaks at T+0.002 sec and ends at T+0.015 sec.  There is a hint
of a second pulse around T+0.01 s.  T90 (15-350 keV) is ~0.01 sec.
  
The time-averaged spectrum from T+0.00 to T+0.01 sec fit by a simple
power-law model shows the power law index of 3.17 +- 0.63
(chi squared 51.9 for 57 d.o.f.).  The fluence in the 15-150 keV band is
2.9 +- 1.1 x 10^-9 erg/cm2.  The 1-sec peak photon flux measured from
T+0.00 sec in the 15-150 keV band is 8.7 +- 3.1 ph/cm2/sec.

A single blackbody fit to the time-averaged spectrum shows the blackbody
temperature of 5.5 +- 0.9 keV (chi squared 43.2 for 57 d.o.f.).  A thermal
bremsstrahlung model fit shows the temperature of 15.8 +- 6.5 keV
(chi squared 48.7 for 57 d.o.f.).  All the quoted errors are at the 90%
confidence level.
  
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/960986/BA/