TITLE:   GCN CIRCULAR
NUMBER:  21630
SUBJECT: Konus-Wind observation of GRB 170816A
DATE:    17/08/21 10:56:48 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred@mail.ioffe.ru>

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

The short/hard GRB 170816A
(Fermi GBM detection: Roberts et al., GCN 21504;
IPN triangulation: Kozlova et al., GCN 21517;
CALET Gamma-Ray Burst Monitor detection: Ishizaki et al., GCN 21615)
triggered Konus-Wind at T0=51789.108 s UT (14:23:09.108).

The burst light curve shows a bright, multi-peaked pulse
which started at ~T0-0.064 s and had a total duration of ~0.3 s.
A weaker count rate increase is also visible around ~T0+1.5 s
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst had a fluence of
6.6(-2.4, +4.2)x10^-6 erg/cm2 and a 16-ms peak energy flux,
measured from T0+0.175s of (5.9 ± 0.7)x10^-5 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 15 MeV range by a cutoff power-law
(CPL) function with the following model parameters:
the photon index alpha = -0.87(-0.36,+0.60),
and the peak energy Ep = 1156(-556,+1626) keV,
chi2 = 86/98 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep, and an upper limit on beta of -1.9,
chi2 = 86/97 dof.

The spectrum near the peak count rate (measured from T0+0.128
to T0+0.192 s) is best fit in the 20 keV - 15 MeV range
by the CPL function with the following model parameters:
the photon index alpha = +0.49(-0.50,+0.66),
and the peak energy Ep = 1339(-285,+462) keV,
chi2 = 17/19 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep, and an upper limit on beta of -1.6,
chi2 = 17/18 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170816_T51789/

All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.

[GCN OPS NOTE(21aug17): Per R.Hamberg's request, in the 2ndline
the Hamburg citation was changed to Roberts.]