TITLE:   GCN CIRCULAR
NUMBER:  35256
SUBJECT: Konus-Wind detection of GRB 231129C
DATE:    23/12/04 15:14:55 GMT
FROM:    Alexandra Lysenko at Ioffe Institute <alexandra.lysenko@mail.ioffe.ru>

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

The bright long-duration GRB 231129C
(Fermi-GBM detection: Sharma et al., GCN Circ. 35227;
MAXI/GSC detection: Kawakubo et al., GCN Circ. 35223;
CALET detection: Kawakubo et al., GCN Circ. 35228;
AstroSat CZTI detection: Waratkar et al., GCN Circ. 35230;
GECAM-B detection: Zheng et al., GCN Circ. 35231;
Swift-XRT detection: Gropp et al., GCN Circ. 35234;
Glowbug detection: Cheung et al., GCN Circ. 35235;
GRBAlpha detection: Dafcikova et al., GCN Circ. 35236;
Fermi-LAT detection: Arimoto et al., GCN Circ. 35238;
AGILE detection: Panebianco et al., GCN Circ. 35244)
triggered Konus-Wind at T0=69016.319 s UT (19:10:16.319).

The burst light curve shows a bright, multi-peaked pulse
featuring a very strong hard-to-soft spectral evolution.
The pulse starts at ~T0-0.2 and has a total duration of ~9.6 s.
The emission is seen up to ~15 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB231129_T69016/

As observed by Konus-Wind, the burst
had a fluence of 8.60(-0.23,+0.24)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+0.106s,
of 4.16(-0.52,+0.54)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+12.800 s)
is best fit in the 20 keV - 20 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.17(-0.06,+0.06),
the high energy photon index beta = -2.95(-0.12,+0.10),
the peak energy Ep = 202(-6,+6) keV
(chi2 = 151/97 dof).

The spectrum near the maximum count rate
(measured from T0 to T0+0.256 s)
is best fit in the 20 keV - 20 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.20(-0.14,+0.15)
and Ep = 782(-52,+55) keV (chi2 = 69/51 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.3
(chi2 = 69/50 dof).

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