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GCN Circular 13758

Subject
Konus-Wind observation of GRB 120911B
Date
2012-09-13T06:51:03Z (12 years ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
S. Golenetskii, R.Aptekar, D. Frederiks, E. Mazets, V. Pal'shin,
P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf
of the Konus-Wind team, report:

The long-duration intense hard GRB 120911B
(IPN detection and localization: Hurley at al., GCN 13755;
Fermi-LAT detection: Racusin et. al., GCN 13756;
Fermi-GBM observation: Gruber et. al., GCN 13757)
triggered Konus-Wind at T0=23172.213s UT (06:26:12.213)

The light curve shows a bright hard pulse with a duration
of ~30 s followed by a tail of weaker and softer extended
emission during the next ~150 s; additionally,
a soft weak precursor is observed around T0-55 s.
The emission in the main bursting episode is seen up to 9 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB120911_T23172/

As observed by Konus-Wind, the burst
had a fluence of 3.0(-0.1,+0.1)x10-4 erg/cm2,
and a 64-ms peak flux, measured from T0+15.232 s,
of 3.8(-0.4,+0.4)x10-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the main emission episode
(measured from T0 to T0+34.048 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.86 (-0.03, +0.03),
the high energy photon index beta = -2.6 (-0.2, +0.2),
the peak energy Ep = 950(-50, +50) keV,
chi2 = 78.4/82 dof.

The spectrum at the maximum count rate
(measured from T0+14.080 to T0+15.616 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.63 (-0.08, +0.09),
the high energy photon index beta = -2.9 (-1.6, +0.3),
the peak energy Ep = 1000(-120, +130) keV,
chi2 = 81.1/82 dof.


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