GCN Circular 23128

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

The long-duration GRB 180809B
(Swift-BAT detection: Moss et al., GCN Circ. 23105
Not found
 
 
;
CALET-GBM detection: Cherry, et al., GCN Circ. 23116
Not found
 
 
)
triggered Konus-Wind at T0=73730.033 s UT (20:28:50.033).

The burst light curve shows a bright multi-peaked emission episode
which starts at ~T0-4 s and has a duration of ~80 s, followed by a 
weaker episode at ~T0-205 s. The total burst duration is ~300 s.
The emission is seen up to ~10 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180809_T73730/

As observed by Konus-Wind, the burst
had a fluence of 3.07(-0.30,+0.36)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+37.952 s,
of 2.66(-0.41,+0.42)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+252.672 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.87(-0.10,+0.12),
the high energy photon index beta = -2.44(-0.24,+0.19),
the peak energy Ep = 275(-30,+25) keV
(chi2 = 123/97 dof).

The spectrum near the maximum count rate
(measured from T0+36.608 to T0+38.144 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.77(-0.12,+0.15),
the high energy photon index beta = -2.20(-0.21,+0.15),
the peak energy Ep = 525(-95,+103) keV
(chi2 = 66/68 dof).

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