[vsnet-grb-info 13362] Konus-Wind observation of GRB 130521B

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14698
SUBJECT: Konus-Wind observation of GRB 130521B
DATE:    13/05/23 08:30:43 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 GRB 130521B
(IPN triangulation: Hurley at al., GCN 14696)
triggered Konus-Wind at T0=77073.510s UT (21:24:33.510).

The light curve shows several pulses from ~T0 s to ~T0+20s,
which, at its initial phase, form a quasi-periodic structure
with the period of ~2.5s.
The emission is seen up to ~7 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB130521_77073/

As observed by Konus-Wind, the burst
had a fluence of (1.9 ± 0.15)x10-5 erg/cm2,
and a 64-ms peak flux, measured from T0+0.512s,
of (4.3 ± 0.3)x10-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+22.016 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 = -0.96 ± 0.07,
the high energy photon index beta = -2.9 ± 0.3,
the peak energy Ep = 151 ± 9 keV,
chi2 = 97.6/97 dof.

The spectrum at the maximum count rate
(measured from T0 to T0+5.888 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 = -0.69 ± 0.08,
the high energy photon index beta = -3.6 ± 1.1,
the peak energy Ep = 205 ± 12 keV,
chi2 = 107/97 dof.

For both spectra, we note a hint of counts excess
over the model flux in the spectral channels around ~10 MeV.

All the quoted results are preliminary.