[vsnet-grb-info 12619] Konus-Wind observation of GRB 121118B

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13979
SUBJECT: Konus-Wind observation of GRB 121118B 
DATE:    12/11/21 10:33:10 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred at 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 GRB 121118B
(IPN detection and localization: Hurley et al., GCN 13977)
triggered Konus-Wind at T0=80847.239s UT (22:27:27.239)

The light curve shows multiple pulses with increasing amplitude
in the time interval starting at ~60s before KW trigger and ending at ~T0+40s.
The emission is seen up to 9 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB121118_T80847/

As observed by Konus-Wind the burst
had a fluence of (8.5 ± 0.3)x10-5 erg/cm2,
and a 64-ms peak flux, measured from T0+13.696 s,
of (1.0 ± 0.6)x10-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the triggered part
of the burst (measured T0 to T0+32.512 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 = -1.30 ± 0.05,
the high energy photon index beta = -3.05 ± 0.70,
the peak energy Ep = 520 ± 64 keV,
chi2 = 78.4/82 dof.

The spectrum at the maximum count rate (measured T0+8.448 to T0+16.128 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff (CPL) model, for which:
the photon index alpha = -1.18 ± 0.04
and the peak energy Ep = 599 ± 52 keV,
chi2 = 91.4/83 dof.
Fitting this spectrum with the Band function yields the same
alpha and Ep with only an upper limit for beta <-3.0 (90% conf.)

All the quoted results are preliminary.