[vsnet-grb-info 19539] Konus-Wind observation of GRB 170626B

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21280
SUBJECT: Konus-Wind observation of GRB 170626B
DATE:    17/06/28 14:20:04 GMT
FROM:    Anna Kozlova at Ioffe Institute  <ann_kozlova at mail.ioffe.ru>

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 170626B
(Insight-HXMT observation: Liu et al., GCN 21265;
IPN triangulation: Kozlova et al., GCN 21279)
triggered Konus-Wind at T0=3482.215 s UT (00:58:02.215).

The burst light curve shows a multipeaked structure
started at ~T0-6.1 s with a total duration of ~16.8 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst
had a fluence of 4.12(-0.20,+0.22)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+4.256 s,
of 1.03(-0.18,+0.18)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+14.592 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 = -0.59(-0.13,+0.14)
and Ep = 423(-38,+45) keV (chi2 = 87/99 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 = 87/98 dof)

The spectrum near the maximum count rate
(measured from T0+0.256 to T0+6.400 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model
with  alpha = -0.45(-0.11,+0.12)
and Ep = 429(-30,+35) keV (chi2 = 91/92 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.8
(chi2 = 91/91 dof)

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170626_T03482/

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