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GCN Circular 9553

Subject
Konus-Wind and Konus-RF observations of GRB 090618
Date
2009-06-22T14:41:45Z (15 years ago)
From
Dmitry Frederiks at Ioffe Institute <fred@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 long GRB 090618 (Schady et al. 2009, GCN 9512)
triggered Konus-Wind
at T0=30504.974 s UT (08:28:24.974),
and Konus-RF instrument onboard CORONAS-PHOTON s/c
at T0=30507.060 s UT (08:28:27.060).

The burst light curve shows a smooth multi-peaked structure
with a duration of ~160 s. Significant spectral evolution
was observed during the burst.

-- 
As observed by Konus-Wind the burst had
a fluence of (2.5 � 0.06)x10-4 erg/cm2,
and a 64-ms peak flux measured from T0+63.616 s
of (1.6 � 0.2)x10-5 erg/cm2/s
(both in the 20 keV - 2 MeV energy range).

The time-integrated spectrum of the burst
(from T0 to T0+142 s) can be fitted
(in the 20 keV - 2 MeV range) by GRB (Band) model
for which:
the low-energy photon index alpha = -1.28 � 0.02,
the high energy photon index beta = -2.66(-0.2, +0.14),
the peak energy Ep = 186 � 8 keV (chi2 = 103/60 dof).

The spectrum at the maximum count rate,
measured from T0+62.720 to T0+64.0 s, is well fitted
(in the 20 keV - 2 MeV range) by GRB (Band) model
for which:
the low-energy photon index alpha = -0.99 (-0.06, +0.07),
the high energy photon index beta = -2.29(-0.5, +0.23),
the peak energy Ep = 440 � 70 keV (chi2 = 52/55 dof).

-- 
As observed by Konus-RF the burst
had a fluence of (2.82 � 0.06)x10-4 erg/cm2
(both in the 20 keV - 2 MeV energy range),
and a 500-ms peak flux measured from T0+63.0 s
of (1.6 � 0.1)x10-5 erg/cm2/s
(in the 20 keV - 1.5 MeV energy range).

The time-integrated spectrum of the burst
(from T0-1.4 to T0+113.0 s) can be fitted
(in the 20 keV - 2 MeV range) by GRB (Band) model
for which:
the low-energy photon index alpha = -1.28 � 0.03,
the high energy photon index beta = -3.06(-0.5, +0.3),
the peak energy Ep = 220 � 8 keV (chi2 = 240/132 dof).

The spectrum at the maximum count rate,
measured from T0+63.0 to T0+63.5 s, is well fitted
(in the 20 keV - 1.5 MeV range) by GRB (Band) model
for which:
the low-energy photon index alpha = -0.89 (-0.1, +0.3),
the high energy photon index beta = -2.56(-1.0, +0.6),
the peak energy Ep = 385 (-136, +64) keV (chi2 = 78/74 dof).

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

The light curves of this GRB is available
at http://www.ioffe.ru/LEA/GRBs/GRB090618_T30504/
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