GCN Circular 22770

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

The long-duration GRB 180611A
(IPN Triangulation: Hurley et al., GCN 22767
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 ;
Fermi GBM observation: Bissaldi &�� Meegan, GCN 22768
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 )
triggered Konus-Wind at T0=12541.046 s UT (03:29:01.046).

The burst light curve shows several peaks with a total duration of ~7 s.
The emission is seen up to ~1.5 MeV.

As observed by Konus-Wind, the burst
had a fluence of 4.61(-0.56,+0.72)x10^-6 erg/cm2,
and a 64-ms peak energy flux, measured from T0+0.148 s,
of 5.04(-2.18,+3.14)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+8.448 s)
is best fit in the 20 keV - 1.5 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with�� alpha = -0.80(-0.26,+0.30),
and Ep = 250(-47,+77) keV (chi2 = 52/60 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index:
beta < -2.25 (chi2 = 52/59 dof).

The spectrum near the peak count rate
(measured from T0 to T0+0.256 s)
is best fit in the 20 keV - 20 MeV range
by the power law with exponential cutoff model
with�� alpha = -1.05(-0.29,+0.38),
and Ep = 668(-304,+856) keV (chi2 = 23/19 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index:
beta < -1.80 (chi2 = 23/18 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180611_T12541/

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