TITLE:   GCN CIRCULAR
NUMBER:  23589
SUBJECT: Konus-Wind observation of GRB 181227A
DATE:    18/12/29 22:21:42 GMT
FROM:    Dmitry Svinkin at Ioffe Institute  <svinkin@mail.ioffe.ru>

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

The long-duration, bright GRB 181227A
(Fermi-GBM detection: Bissaldi & Veres, GCN Circ. 23569;
IPN triangulation: Hurley et al., GCN Circ. 23577)
triggered Konus-Wind at T0=22619.317 s UT (06:16:59.317).

The burst light curve shows a single emission episode
which starts at ~T0-0.5 s and has a total duration of ~17 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst
had a fluence of 5.91(-0.12,+0.12)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+8.944 s,
of 1.39(-0.15,+0.16)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+18.688 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.66(-0.07,+0.07),
the high energy photon index beta = -3.53(-0.24,+0.18),
the peak energy Ep = 93(-2,+2) keV
(chi2 = 72/96 dof).

The spectrum near the maximum count rate
(measured from T0+8.192 to T0+8.960 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.35(-0.14,+0.15),
the high energy photon index beta = -4.34(-5.66,+0.70),
the peak energy Ep = 117(-5,+5) keV
(chi2 = 31/46 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB181227_T22619/

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