GCN Circular 46171

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

The bright, short-duration GRB 261029C
(AstroSat-CZTI detection: Harsha et al., GCN 46129
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 ;
IPN triangulation: Svinkin et al., GCN 46159
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 )
triggered Konus-Wind at T0=85117.559 s UT (23:38:37.559).

The burst light curve shows a single bright peak
which starts at ~T0-10 ms and has a duration of ~30 ms,
followed by a weaker emission seen up to ~T0+350 ms.
The emission is seen up to ~10 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB261029_T85117/

As observed by Konus-Wind, the burst
had the total fluence of 8.27(-0.76,+0.80)x10^-6 erg/cm2,
and the 16-ms peak flux, measured from T0-0.006 s,
of 6.57(-1.08,+1.65)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+0.192 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.72(-0.14,+0.16),
the high energy photon index beta = -2.20(-0.59,+0.27),
the peak energy Ep = 1432(-361,+482) keV
(PG-stat = 87/78 dof).

Since a significant fraction of the main peak of the burst light curve
was detected before the trigger, we performed spectral analysis
of the burst peak using the KW 3-channel light curve data.

Modelling the KW 3-channel time-integrated spectrum
(measured from T0-0.010 s to T0+0.018 s)
by a power law with exponential cutoff (CPL) model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep),
yields alpha = -0.70(-0.24,+0.26) and Ep = 645(-140,+300) keV.

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