TITLE:   GCN CIRCULAR
NUMBER:  45990
SUBJECT: Konus-Wind detection of GRB 261017A
DATE:    26/10/19 14:57:57 GMT
FROM:    Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>

A. Ridnaia, D. Frederiks, A. Lysenko, V. Panteleeva,
D. Svinkin, A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The long-duration GRB 261017A
(Fermi-GBM detection: Fermi GBM team, GCN 45973; 
Mukherjee et al., GCN 45976
Swift-BAT detection: Siegel et al., GCN 45974;
Barthelmy et al., GCN 45985)
triggered Konus-Wind at T0=57906.065 s UT (16:05:06.065).

The burst light curve shows a multipeaked structure
which starts at ~T0-2.4 s and has a total duration of ~10.8 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/GRB261017_T57906/

As observed by Konus-Wind, the burst
had the total fluence of 1.96(-0.14,+0.15)x10^-5 erg/cm2,
and the 64-ms peak flux, measured from T0-0.064 s,
of 6.37(-1.28,+1.30)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+8.448 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 = -0.06(-0.16,+0.18)
and Ep = 899(-80,+93) keV (chi2 = 90/89 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 = 90/88 dof).

All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.