TITLE:   GCN CIRCULAR
NUMBER:  20806
SUBJECT: Konus-Wind observation of GRB 170228A
DATE:    17/03/03 13:49:20 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 GRB 170228A
(Fermi-LAT detection: Bissaldi et al., GCN 20785;
Fermi GBM observation: Veres et al., GCN 20786;
AstroSat CZTI detection: Sharma et al., GCN 20788)
triggered Konus-Wind at T0=68584.788 s UT (19:03:04.788).

The burst light curve starts with a bright FRED-like pulse having a
duration of ~20 s, followed by a weaker emission,
which is detectable until ~T0+100 s.
The emission is seen up to ~3 MeV.

As observed by Konus-Wind, the burst
had a fluence of 4.99(-0.99,+1.51)x10^-5 erg/cm2,
and a 64-ms peak energy flux, measured from T0+0.316 s,
of 8.97(-2.47,+2.57)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst
(measured from T0 to T0+98.560 s)
is best fit in the 20 keV - 15 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -1.03(-0.18,+0.22),
and Ep = 1017(-317,+657) keV (chi2 = 97/98 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index:
beta < -1.98 (chi2 = 97/97 dof).

The spectrum near the peak count rate
(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 5 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.43(-0.14,+0.17),
the high energy photon index beta = -2.78(-2.28,+0.48),
the peak energy Ep = 675(-92,+112) keV,
chi2 = 95/76 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170228_T68584/

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