TITLE:   GCN CIRCULAR
NUMBER:  45694
SUBJECT: Konus-Wind detection of GRB 260810A
DATE:    26/09/22 18:17:20 GMT
FROM:    Valentina Panteleeva at Ioffe Institute <panteleevav228@gmail.com>

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

The long-duration GRB 260810A
(AstroSat-CZTI detection: Arya et al., GCN 45363;
Glowbug detection: Cheung et al., GCN 45365;
Insight-HXMT-HE detection: Yu et al., GCN 45392;
SVOM-GRM observation: Guo et  al., GCN 45402;
IPN triangulation: Kozyrev et al., GCN 45627)
triggered Konus-Wind at T0=68985.874 s UT (19:09:45.874).

The burst light curve shows a multipeaked structure
which starts at ~T0-0.4 s and has a total duration of ~26.3 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/GRB260810_T68985/

As observed by Konus-Wind, the burst
had the total fluence of 4.95(-0.28,+0.29)x10^-5 erg/cm2,
and the 64-ms peak flux, measured from T0+9.216 s,
of 1.03(-0.10,+0.10)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+25.856 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 = -0.99(-0.09,+0.10),
the high energy photon index beta = -2.08(-0.06,+0.05),
the peak energy Ep = 187(-19,+20) keV
(chi2 = 70/97 dof).

The spectrum near the maximum count rate
(measured from T0+2.304 to T0+9.472 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 = -1.14(-0.09,+0.10),
the high energy photon index beta = -2.46(-0.12,+0.09),
the peak energy Ep = 129(-9,+10) keV
(chi2 = 56/79 dof).

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