TITLE:   GCN CIRCULAR
NUMBER:  18233
SUBJECT: Konus-Wind observation of GRB 150902A
DATE:    15/09/03 16:00:52 GMT
FROM:    Dmitry Svinkin at Ioffe Institute  <svinkin@mail.ioffe.ru>

S. Golenetskii, R. Aptekar, D. Frederiks, V. Pal'shin, 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-duration, very bright GRB 150902A
(Fermi LAT detection: Arimoto et al., GCN Circ. 18228;
Fermi GBM detection: Roberts and Younes, GCN Circ. 18229)
triggered Konus-Wind at T0=63340.850 s UT (17:35:40.850).

The burst light curve shows a single pulse with
a total duration of ~20 s followed by a weak tail up to ~100 s.
The emission is seen up to ~18 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB150902_T63340/

As observed by Konus-Wind, the burst
had a fluence of 1.21(-0.07,+0.07)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+6.384 s,
of 2.13(-0.27,+0.28)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+25.600 s)
is best fit in the 20 keV - 18 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.58(-0.06,+0.07),
the high energy photon index beta = -2.30(-0.11,+0.09),
the peak energy 322(-21,+23) keV
(chi2 = 138/96 dof)

The spectrum near the maximum count rate
(measured from T0+6.144 to T0+6.656 s)
is best fit in the 20 keV - 11 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.02(-0.18,+0.21),
the high energy photon index beta = -2.75(-0.39,+0.23),
the peak energy 288(-33,+37) keV
(chi2 = 77/47 dof)

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