[vsnet-grb-info 18841] Konus-Wind observation of GRB 161218A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20292
SUBJECT: Konus-Wind observation of GRB 161218A
DATE:    16/12/19 12:03:31 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred at mail.ioffe.ru>

D. Frederiks, S. Golenetskii, R.Aptekar, P. Oleynik, M. Ulanov,
D. Svinkin, A. Tsvetkova, A.Lysenko, A. Kozlova, and T. Cline,
on behalf of the Konus-Wind team, report:

The long GRB 161218A (Swift-BAT detection: D'Ai et al., GCN 20283;
POLAR observation: Li et al., GCN 20287)
triggered Konus-Wind at T0=13651.970 s UT (03:47:31.970).

The burst light curve shows a single pulse with a total duration
of ~7 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst had a fluence of
(1.24 ± 0.10)x10^-5 erg/cm2 and a 64-ms peak energy flux,
measured from T0+0.640, of (4.6 ± 0.4)x10^-5 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+10.496 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.28 (-0.21,+0.25),
the high energy photon index beta = -3.40 (-1.17,+0.43),
the peak energy Ep = 128 (-8,+8) keV,
chi2 = 110/97 dof.

The spectrum near the peak count rate (measured from T0+0.256
to T0+2.304 s) is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = +0.08 (-0.26,+0.29),
the high energy photon index beta = -3.18 (-0.59,+0.31),
the peak energy Ep = 135 (-9,+10) keV,
chi2 = 84/74 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB161218_T13651/

All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.