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GCN Circular 23557

Subject
Konus-Wind observation of GRB 181222B
Date
2018-12-25T10:36:09Z (5 years ago)
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 short-duration, extremely bright GRB 181222B
(Fermi-GBM detection: Veres, GCN Circ. 23551;
IPN triangulation: Svinkin et al., GCN Circ. 23556)
triggered Konus-Wind at T0=72694.563 s UT (20:11:34.563).

The burst light curve shows a single pulse
which starts at about T0 and has a total duration of ~2.1 s.
The emission is seen up to ~15 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB181222_T72694/

As observed by Konus-Wind, the burst
had a fluence of 3.70(-0.17,+0.18)x10^-5 erg/cm2,
and a 16-ms peak flux, measured from T0+0.166 s,
of 2.72(-0.25,+0.26)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+0.512 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 = -0.52(-0.08,+0.08),
the high energy photon index beta = -2.95(-0.30,+0.20),
the peak energy Ep = 365(-26,+27) keV
(chi2 = 53/56 dof).

Among ~300 bursts from the Konus catalog of short GRBs
(Svinkin et al., ApJS 224, 10, 2016), GRB 181222B is within top 2%
in the terms of 16-ms peak energy flux and within top 2% in the terms
of the total energy fluence, both in the 20 keV - 10 MeV range.

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