TITLE:   GCN CIRCULAR
NUMBER:  23240
SUBJECT: Konus-Wind of the very bright GRB 180914B
DATE:    18/09/16 14:34:47 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred@mail.ioffe.ru>

D. Frederiks, S. Golenetskii, R.Aptekar, A. Kozlova,
A.Lysenko,  D. Svinkin, A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The long, very bright GRB 180914B
(Agile/MCAL detection: Ursi et al., GCN 23226;
Fermi-LAT detection: Bissaldi & Longo, GCN 23232,
Agile/GRID detection: Verrecchia et al., GCN 23233)
triggered Konus-Wind (KW) at T0=66182.692 s UT (18:23:02.692).

The burst light curve shows multiple pulses in the interval from
T0 - 30 s to T0+250 s. A total duration of the burst (T100)
is ~280 s. The emission is seen up to ~15 MeV.

As observed by Konus-Wind, the burst had a fluence of
(1.15 ± 0.05)x10^-3 erg/cm2 and a 64-ms peak energy flux,
measured from T0+5.824, of (1.14 ± 0.24)x10^-4 erg/cm2
(both in the 20 keV - 10 MeV energy range).
The fluence of GRB 180914B is among the highest measured
for the Konus-Wind sample of >3000 GRBs detected since 1994.

The time-integrated spectrum (measured from T0 to T0+168.192 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 = -0.81 (-0.04,+0.04),
the high energy photon index beta = -2.12 (-0.7,+0.08),
the peak energy Ep = 466 (-27,+29) keV
(chi2 = 104/97 dof).

The spectrum near the peak count rate (measured from T0+5.632 s
to T0+6.144 s) is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
alpha = -0.64 (-0.08,+0.10),
beta = -1.98 (-0.16,+0.12),
Ep = 1285 (-249,+287) keV
(chi2 = 68/69 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180914_T66182/

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