GCN Circular 19810

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, very intense, GRB 160816A
(Fermi LAT detection: Racusin et al., GCN Circ. 19802
Not found
 
 
;
Fermi GBM observation: Mailyan and Meegan, GCN Circ. 19804
Not found
 
 
)
triggered Konus-Wind at T0=63061.653 s UT (17:31:01.653).

The burst light curve shows a multipeaked structure
started at ~T0 with a total duration of ~14 s.
The emission is seen up to 3 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB160816_T63061/

As observed by Konus-Wind, the burst
had a fluence of 3.16(-0.10,+0.11)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+8.032 s,
of 1.63(-0.16,+0.16)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+19.712 s)
is best fit in the 20 keV - 3 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.81(-0.06,+0.06)
and Ep = 239(-11,+12) keV (chi2 = 51/68 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.0
(chi2 = 49/67 dof)

The spectrum near the maximum count rate
(measured from T0+2.304 to T0+8.448 s)
is best fit in the 20 keV - 3 MeV range
by a power law with exponential cutoff model
with  alpha = -0.89(-0.08,+0.09)
and Ep = 244(-18,+20) keV (chi2 = 66/68 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.2
(chi2 = 66/67 dof)

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