TITLE:   GCN CIRCULAR
NUMBER:  45729
SUBJECT: Konus-Wind detection of GRB 260922A
DATE:    26/09/24 16:37:49 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 260922A
(Swift detection: Page et al., GCN 45690;
Sakamoto et al., GCN 45703;
CALET-GBM detection: Ricciarini et al., GCN 45716;
NuSTAR detection: Waratkar & Grefenstette, GCN 45728)
triggered Konus-Wind at T0=36035.366 s UT (10:00:35.366).

The burst light curve shows a multi-peaked emission pulse,
which starts at ~T0-3.5 s and has a total duration of ~15.6 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/GRB260922_T36035/

As observed by Konus-Wind, the burst
had the total fluence of 6.88(-0.28,+0.29)x10^-6 erg/cm2,
and the 64-ms peak flux, measured from T0+1.552 s,
of 2.15(-0.35,+0.35)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 - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.31(-0.19,+0.21)
and Ep = 151(-9,+10) keV (chi2 = 101/98 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.6
(chi2 = 101/97 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 - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.39(-0.15,+0.16)
and Ep = 153(-8,+8) keV (chi2 = 63/83 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.9
(chi2 = 62/82 dof).

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