TITLE:   GCN CIRCULAR
NUMBER:  22291
SUBJECT: Konus-Wind observation of GRB 171227A
DATE:    17/12/29 13:52:39 GMT
FROM:    Anastasia Tsvetkova at Ioffe Institute  <tsvetkova@mail.ioffe.ru>

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

The long-duration, hard-spectrum, very intense GRB 171227A
(AGILE/MCAL detection: Verrecchia et al., GCN 22288;
Fermi GBM detection: Hui, GCN 22289;
IPN Triangulation: Kozlova et al., GCN 22290)
triggered Konus-Wind at T0=9.491 s UT (00:00:09.491).
The burst light curve shows a multi-peaked structure
with a total duration of ~56 s.
The emission is seen up to ~19 MeV.

As observed by Konus-Wind, the burst
had a fluence of 6.31(-0.19,+0.19)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+18.880 s,
of 1.19(-0.10,+0.10)x10^-4 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+60.416 s)
is best fit in the 20 keV - 19 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.87(-0.03,+0.03),
the high energy photon index beta = -2.12(-0.06,+0.05),
the peak energy Ep = 618(-35,+38) keV
(chi2 = 139/97 dof)

The spectrum near the maximum count rate
(measured from T0+18.176 to T0+18.944 s)
is best fit in the 50 keV - 19 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.77(-0.07,+0.08),
the high energy photon index beta = -2.38(-0.26,+0.16),
the peak energy Ep = 1498(-215,+262) keV
(chi2 = 62/73 dof)

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB171227_T00009/

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