TITLE:   GCN CIRCULAR
NUMBER:  9171
SUBJECT: Konus-Wind observation of GRB 090418B
DATE:    09/04/20 13:30:41 GMT
FROM:    Valentin Pal'shin at Ioffe Inst  <val@mail.ioffe.ru>

S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, P.
Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind
team report:

The long Swift-BATSS GRB 090418B (Copete et al., GCN 9159)
triggered Konus-Wind at T0=32366.325 s UT (08:59:26.325).

The burst light curve shows a soft weak precursor at ~T0-20 s, the main 
multipeaked pulse at T0 with a duration of ~45 s, and a weak soft pulse 
at ~T0+70 with a duration of ~30 s (the same lc structure was seen by 
BAT: Copete et al., GCN 9159).

As observed by Konus-Wind the burst
had a fluence of (2.31 +/- 0.09)x10^-5 erg/cm2,
and a 256-ms peak flux measured from T0+15.840 s
of (1.54 +/- 0.20)x10^-6 erg/cm2/s
(both in the 20 keV - 1 MeV energy range).

The time-integrated spectrum of the burst
(from T0 to T0+40.704 s) can be fitted (in the 20 keV-1 MeV range)
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -1.23(-0.09, +0.010),
and Ep = 117(-7, +8) keV (chi2 = 62.0/56 dof).
Fitting by GRB (Band) model yields the same alpha and Ep,
and only an upper limit on the high energy
photon index: beta < -3.18 (chi2 = 62.0/55 dof).

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

The Konus-Wind light curve of this GRB is available
at http://www.ioffe.ru/LEA/GRBs/GRB090418_T32366/