[vsnet-grb-info 13019] Konus-Wind observation of GRB 130320B

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14356
SUBJECT: Konus-Wind observation of GRB 130320B
DATE:    13/03/30 11:59:08 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 very long intense GRB 130320B
(IPN triangulation: Hurley et al., GCN 14354)
triggered Konus-Wind at T0=48251.726s UT (13:24:11.726)

The burst consists of three emission episodes with a total duration of ~380 s.
The first episode (from ~T0-1 to ~T0+15s) shows very bright
multi-peaked pulse with strong hard-to-soft spectral evolution.
The second episode is a single weak soft-spectrum pulse
from T0+135 to T0+175s. The third episode (from ~T0+195 to ~T0+380s)
also shows a single pulse, more intense and harder than the second one.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB130320_T48251/

As observed by Konus-Wind, the burst
had a total fluence of (7.8 ± 0.3)x10-5 erg/cm2,
and a 64-ms peak flux, measured from T0+0.704s,
of (7.2 ± 1.8)x10-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+384.768 s)
is best fit in the 20 keV - 15 MeV range
by a simple power law with the photon index 2.24 ± 0.03,
chi2 = 85.5/98 dof.

The spectrum at the onset of the burst (measured from T0 to T0+0.256 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -1.0 ± 0.3,
the high energy photon index beta = -2.0 ± 0.3,
the peak energy Ep = 340 ± 190 keV,
chi2 = 23/25 dof.

The average spectrum of the second emission episode
(measured from T0+139.008 to T0+188.160 s)
is best fit in the 20 keV - 2 MeV range
by a power law with exponential cutoff model,
for which:
alpha = -1.7 ± 0.3,
and Ep = 46 ± 23 keV,
chi2 = 47/58 dof.

The average spectrum of the third emission episode
(measured from T0+294.656 to T0+384.768 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -1.23 ± 0.17,
the high energy photon index beta = -2.25 ± 0.19,
the peak energy Ep = 156 ± 29 keV,
chi2 = 91.6/96 dof.


All the quoted results are preliminary.