TITLE:   GCN CIRCULAR
NUMBER:  22142
SUBJECT: Konus-Wind observation of GRB 171120A
DATE:    17/11/21 12:48:30 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred@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 171120A (Swift/BAT detection: Tohuvavohu et al., GCN 22133; 
Stamatikos et al., GCN 22139; Fermi-LAT detection: Longo et al.,
GCN 22136; Fermi-GBM detection: Stanbro et al., GCN 22138)
triggered Konus-Wind at T0=48000.683 s UT (13:20:00.683).

The KW light curve shows two separate emission episodes.
A total duration of the burst is ~44 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst had a fluence of
1.7(-0.3,+0.5)x10^-5 erg/cm2 and a 64-ms peak energy flux,
measured from T0+1.644, of (1.29 ± 0.13)x10^-5 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+49.408 s)
is best fit in the 20 keV - 15 MeV range by a cutoff power-law
(CPL) function with the following model parameters:
the photon index alpha = -1.59(-0.19,+0.23),
and the peak energy Ep = 200(-56,+183) keV,
chi2 = 84/98 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep, and an upper limit on beta of -2.0.

The spectrum near the peak count rate (measured from T0+0.128
to T0+0.256 s) is best fit in the 20 keV - 15 MeV range by
the CPL function with the following model parameters:
the photon index alpha = -0.33(-0.30,+0.35),
and the peak energy Ep = 305(-41,+53) keV,
chi2 = 39/36 dof.
Fitting this spectrum with the GRB (Band) function yields
similar alpha and Ep, and an upper limit on beta of -2.7.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB171120_T48000/

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