TITLE:   GCN CIRCULAR
NUMBER:  22621
SUBJECT: Konus-Wind observation of GRB 180409A
DATE:    18/04/10 10:00:09 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred@mail.ioffe.ru>

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

The long GRB 180409A (IPN Triangulation: Hurley et al., GCN 22619)
triggered Konus-Wind at T0=29904.770 s UT (08:18:24.770)

The burst light curve shows a multi-peaked structure,
which started at ~T0-3 s and peaked at ~T0+9.4 s.
The total duration of the burst is ~20 s.
The emission is seen up to ~3 MeV.

As observed by Konus-Wind, the burst had a fluence of
(8.8 ± 1.3)x10^-6 erg/cm2 and a 64-ms peak energy flux,
measured from T0+9.408, of (9.9 ± 1.5)x10^-6 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+17.920 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 = -0.96 (-0.09,+0.10),
the high energy photon index beta = -3.1 (-6.9,+0.42),
the peak energy Ep = 180 (-14,+15) keV,
chi2 = 67/97 dof.

The spectrum near the peak count rate (measured from T0+7.936
to T0+9.728 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 = -0.50 (-0.13,+0.20),
the high energy photon index beta = -3.5 (-6.5,+0.8),
the peak energy Ep = 266 (-35,+26) keV,
chi2 = 81/78 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180409_T29904/

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