TITLE:   GCN CIRCULAR
NUMBER:  20547
SUBJECT: Konus-Wind observation of GRB 170126A
DATE:    17/01/27 18:44:30 GMT
FROM:    Anna Kozlova at Ioffe Institute  <ann_kozlova@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 170126A
(Swift-BAT detection: Kocevski et al., GCN 20530;
Fermi-GBM observation: Bissaldi, GCN 20533;
AstroSat CZTI detection: Sharma et al., GCN 20537)
triggered Konus-Wind at T0=41440.253 s UT (11:30:40.253).

The burst light curve shows a single pulse
started at ~T0-0.5 s with a total duration of ~28 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/GRB170126_T41440/

As observed by Konus-Wind, the burst
had a fluence of 8.25(-0.81,+0.94)x10^-6 erg/cm2,
and a 64-ms peak flux, measured from T0+0.992 s,
of 2.87(-0.85,+0.87)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+16.640 s)
is best fit in the 20 keV - 2 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.98(-0.22,+0.24)
and Ep = 188(-27,+40) keV (chi2 = 54/59 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 = 54/58 dof)

The spectrum near the maximum count rate
(measured from T0+0.256 to T0+8.448 s)
is best fit in the 20 keV - 2 MeV range
by a power law with exponential cutoff model
with  alpha = -1.03(-0.17,+0.18)
and Ep = 206(-27,+37) keV (chi2 = 40/58 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.4
(chi2 = 40/57 dof)

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