[vsnet-grb-info 18279] Konus-Wind observation of GRB 160720A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19727
SUBJECT: Konus-Wind observation of GRB 160720A
DATE:    16/07/21 18:15:18 GMT
FROM:    Dmitry Svinkin at Ioffe Institute  <svinkin at mail.ioffe.ru>

D. Svinkin, S. Golenetskii, R. Aptekar, D. Frederiks, P. Oleynik,
M. Ulanov,  A. Tsvetkova, A. Lysenko, A. Kozlova, and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration GRB 160720A
(Fermi-GBM detection: Hamburg and Burns, GCN Circ. 19724;
IPN triangulation: Hurley et al., GCN Circ. 19726)
triggered Konus-Wind at T0=66314.254 s UT (18:25:14.254).

The burst light curve shows a multipeaked structure
started at ~T0-80 s with a total duration of ~160 s.
The emission is seen up to ~2 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB160720_T66314/

As observed by Konus-Wind, the burst
had a fluence of 1.50(-0.05,+0.05)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+10.288 s,
of 1.31(-0.16,+0.16)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the most intense part
(measured from T0 to T0+27.392 s)
is best fit in the 20 keV - 3 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.87(-0.04,+0.04),
the high energy photon index beta = -2.87(-0.18,+0.14),
the peak energy Ep = 227(-8,+9) keV
(chi2 = 108/75 dof)

The spectrum near the maximum count rate
(measured from T0+9.728 to T0+10.496 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.82(-0.08,+0.09)
and Ep = 328(-28,+32) keV (chi2 = 66/54 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.7
(chi2 = 66/53 dof)

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