TITLE:   GCN CIRCULAR
NUMBER:  20865
SUBJECT: Konus-Wind observation of GRB 170311B
DATE:    17/03/14 09:18:29 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, very intense GRB 170311B (IPN triangulation:
Hurley et al., GCN 20859) triggered Konus-Wind
at T0=49504.661 s UT (13:45:04.661).

The burst light curve shows a bright, multi-peaked structure,
that is preceded and followed by a weaker emission.
The total duration of the burst is ~30 s.
The emission is seen up to ~8 MeV.

As observed by Konus-Wind, the burst had a fluence of
(8.0 ± 0.6)x10^-5 erg/cm2 and a 64-ms peak energy flux,
measured from T0+5.888, of (2.5 ± 0.3)x10^-5 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+15.360 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.61 (-0.06,+0.06),
the high energy photon index beta = -2.85 (-0.49,+0.25),
the peak energy Ep = 440 (-28,+30) keV,
chi2 = 105/97 dof.

The spectrum near the peak count rate (measured from T0+4.608
to T0+6.114 s) is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.48 (-0.12,+0.13),
the high energy photon index beta = -2.60 (-0.44,+0.23),
the peak energy Ep = 408 (-48,+55) keV,
chi2 = 67/74 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170311_T49504/

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