[vsnet-grb-info 20188] Konus-Wind observation of GRB 171216B

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22284
SUBJECT: Konus-Wind observation of GRB 171216B
DATE:    17/12/25 15:37:42 GMT
FROM:    Dmitry Svinkin at Ioffe Institute  <svinkin at mail.ioffe.ru>

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

The long-duration, hard-spectrum GRB 171216B
(IPN triangulation: Hurley et al., GCN circ. 22263;
CALET-CGBM detection: Pal'shin et al., GCN circ. 22268)
triggered Konus-Wind at T0=51948.499 s UT (14:25:48.499).

The burst light curve shows a multipeaked structure
which starts at ~T0-0.3 s and has a total duration of ~7.4 s.
The emission is seen up to ~5 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB171216_T51948/

As observed by Konus-Wind, the burst
had a fluence of 1.59(-0.29,+0.37)x10^-5 erg/cm2,
and a 16-ms peak flux, measured from T0+0.034 s,
of 2.32(-1.00,+1.15)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -1.11(-0.11,+0.13)
and Ep = 1341(-412,+673) keV (chi2 = 85/98 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.3
(chi2 = 85/97 dof).

The spectrum near the maximum count rate
(measured from T0 to T0+0.064 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
with  alpha = -0.34(-0.37,+0.52)
and Ep = 994(-372,+539) keV (chi2 = 15/16 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.2
(chi2 = 15/15 dof).

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.