[vsnet-grb-info 13811] Konus-Wind observation of GRB 130821A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15125
SUBJECT: Konus-Wind observation of GRB 130821A
DATE:    13/08/26 16:46:37 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred at mail.ioffe.ru>

S. Golenetskii, R.Aptekar, D. Frederiks, 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 130821A
(Fermi-GBM detection: Jenke, GCN 15113;
Fermi-LAT detection: Kocevski, et al., GCN 15115)
triggered Konus-Wind at T0=58258.022 s UT (16:10:58.022).

The light curve shows multiple pulses from ~T0-40 to ~T0+80 s.
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/GRB130821_T58258/

As observed by Konus-Wind, the burst
had a fluence of (9.9 ± 0.9)x10-5 erg/cm2,
and a 64-ms peak flux, measured from T0+6.784 s,
of (1.3 ± 0.1)x10-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum (measured from T0 to T0+78.080 s)
is best fit in the 20 keV - 18 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -1.33 ± 0.11,
the high energy photon index beta = -2.25 ± 0.19,
the peak energy Ep = 260 ± 47 keV,
chi2 = 84.6/97 dof.

The spectrum at the maximum count rate
(measured from T0 to T0+12.544 s)
is best fit in the 20 keV - 18 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -1.11 ± 0.07,
the high energy photon index beta = -2.33 ± 0.10,
the peak energy Ep = 255 ± 22 keV,
chi2 = 96.9/97 dof.

All the quoted results are preliminary.