[vsnet-grb-info 17775] GRB 160321A: Swift-BAT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19216
SUBJECT: GRB 160321A: Swift-BAT refined analysis
DATE:    16/03/22 14:47:19 GMT
FROM:    Takanori Sakamoto at AGU  <tsakamoto at phys.aoyama.ac.jp>

H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):

Using the data set from T-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 160321A (trigger #680017)
(Stamatikos, et al., GCN Circ. 19211).  The BAT ground-calculated position is
RA, Dec = 99.420, 5.753 deg which is
     RA(J2000)  =  06h 37m 40.7s
     Dec(J2000) = +05d 45' 09.3"
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 96%.

The mask-weighted light curve shows a single-pulse structure that starts
at ~ T0-22 sec, peaks at ~ T+2 sec, and ends at ~ T+23 sec.
T90 (15-350 keV) is 33.6 +- 4.8 sec (estimated error including systematics).

The time-averaged spectrum from T-20.9 to T+19.0 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.89 +- 0.19.  The fluence in the 15-150 keV band is 5.3 +- 0.7 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+2.17 sec in the 15-150 keV band
is 0.5 +- 0.1 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

Based on the ground analysis result, this event is very likely a GRB.
However, given that it is on the Galactic Plane (lat = -0.43 deg.),
we cannot rule out a galactic origin.  We note that the BAT time averaged
spectrum is soft but still in the typical range for BAT GRBs.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/680017/BA/