GCN Circular 21278

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

The long-duration GRB 170626A (Swift-BAT trigger #758766:
Marshall et al., GCN 21264
Not found
 
 
; Barthelmy et al., GCN 21271
Not found
 
 
;
Fermi GBM observation: Hamburg et al., GCN 21266
Not found
 
 
;
Insight-HXMT observation: Xu et al., GCN 21274
Not found
 
 
)
triggered Konus-Wind at T0=34640.048 s UT (09:37:20.048).

The burst light curve shows a multipeaked structure
started at ~T0-0.4 s with a total duration of ~12.8 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst
had a fluence of 1.22(-0.05,+0.05)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+0.576 s,
of 6.70(-0.97,+0.98)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+15.360 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 = -1.23(-0.10,+0.11)
and Ep = 110(-7,+8) keV (chi2 = 92/99 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
the high energy photon index beta = -3.3 (-0.9,+0.4)
(chi2 = 90/98 dof)

The spectrum near the maximum count rate
(measured from T0+0.256 to T0+7.168 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model
with  alpha = -1.17(-0.10,+0.11)
and Ep = 123(-8,+9) keV (chi2 = 78/95 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
the high energy photon index beta = -3.5 (-3.1,+0.4)
(chi2 = 77/94 dof)

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170626_T34640/

All the quoted errors are at the 90% confidence level,
except for beta errors, which are at the 68% confidence level.
All the quoted values are preliminary.