[vsnet-grb-info 18842] GRB 161218A: Swift-BAT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20293
SUBJECT: GRB 161218A: Swift-BAT refined analysis
DATE:    16/12/19 13:48:29 GMT
FROM:    Takanori Sakamoto at AGU  <tsakamoto at phys.aoyama.ac.jp>

C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC), J. R. Cummings (CPI),
A. D'Ai (INAF-IASFPA), N. Gehrels (GSFC),H. A. Krimm (NSF/USRA),
A. Y. Lien (GSFC/UMBC), 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-352 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 161218A (trigger #727288)
(D'Ai, et al., GCN Circ. 20283).  The BAT ground-calculated position is
RA, Dec = 245.250, -4.113 deg which is
    RA(J2000)  =  16h 21m 00.1s
    Dec(J2000) = -04d 06' 46.3"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 60%.

The mask-weighted light curve shows a bright FRED-like peak starting
from T-2 sec, peaking at T+1 sec and ending at T+14 sec.  A possible
extended emission is evident in the 10-sec binning light curve lasting
until T+80 sec.  T90 (15-350 keV) is 7.1 +- 0.6 sec (estimated error
including systematics).

The time-averaged spectrum from T-1.4 to T+14.5 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.56 +- 0.16,
and Epeak of 117 +- 13 keV (chi squared 38.16 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 6.7 +- 0.1 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+0.27 sec in the 15-150 keV band is
17.6 +- 0.5 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.29 +- 0.03 (chi squared 111.22 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/727288/BA/