[vsnet-grb-info 7563] Konus-Wind and Konus-RF observations of GRB 090408b

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9121
SUBJECT: Konus-Wind and Konus-RF observations of GRB 090408b
DATE:    09/04/10 14:40:32 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred at mail.ioffe.ru>

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


The very bright long GRB 090408b  triggered Konus-Wind
at T0=71198.539 s UT (19:46:38.539),
and Konus-RF instrument onboard CORONAS-PHOTON s/c
at T0=71203.482 s UT (19:46:43.482).

We have triangulated this burst to a preliminary
Konus-Wind - Konus-RF annulus centered at
RA(2000)=41.01, Dec(2000)=+14.92,
whose radius is 11.6 ± 1.3 deg (3 sigma).

The Konus-Wind and Konus-RF light curves of this GRB are available
at http://www.ioffe.ru/LEA/GRBs/GRB090408_T71198/
They show a multipeaked structure with a duration of ~8 s.
The burst demonstartes strong spectral evolution,
as observed by Konus-RF a hard part of the burst emission
(above 500 keV) consists of several relatively narrow peaks,
while soft emission time profile is more smooth.
No emission is seen above 2500 kev.

The time-integrated spectrum of the most intense part of the event
(measured by Konus-Wind from T0 to T0+5.632 s)
can be fitted (in the 20 - 2500 keV range) by GRB (Band) model for which:
the low-energy photon index alpha = -0.67(-0.04, +0.04),
the high energy photon index beta = -2.68(-0.09, +0.08),
the peak energy Ep = 344(-14, +13) keV (chi2 = 107/61 dof).

The spectrum of the most intense peak
(measured by Konus-Wind from T0+2.816 to T0+3.082 s)
is well fitted (in the 20 - 2500 keV range) by GRB (Band) model for which:
the low-energy photon index alpha = -0.49 +/-0.09,
the high energy photon index beta = -2.94 (-0.28, +0.20),
the peak energy Ep = (431 +/- 30) keV (chi2 = 54/61 dof).

The burst had a fluence of (2.84 +/- 0.17)x10-4 erg/cm2,
and a 16-ms peak flux measured from T0+2.912 s
of 3.4(-0.8, +0.6)x10-4 erg/cm2/s
(both in the 20 - 2500 keV energy range).

Due to uncertainties in the burst incident angles
the quoted values are preliminary.
All the quoted errors are at the 90% confidence level.