TITLE:   GCN CIRCULAR
NUMBER:  46136
SUBJECT: Konus-Wind detection of GRB 261029A
DATE:    26/11/03 10:53:09 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 261029A
(Fermi-GBM detection: The Fermi GBM team, GCN 46071;
Scotton, GCN 46098;
SVOM-ECLAIRs detection: Goto et al., GCN 46072;
Fermi-LAT detection: Longo et al., GCN 46085;
AstroSat CZTI detection: Salunke et al., GCN 46089;
CALET detection: Marrocchesi et al., GCN 46095;
SVOM-GRM observation: Yu et al., GCN 46096;
NuSTAR detection: Waratkar & Grefenstette, GCN 46100;
GECAM-B detection: Yu & Xiong, GCN 46108;
Glowbug detection: Cheung et al., GCN 46112)
triggered Konus-Wind at T0=05228.129 s UT (01:27:08.129).

The burst light curve shows a multipeaked structure
which starts at ~T0-0.4 s and has a total duration of ~112 s.
The emission is seen up to ~60 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB261029_T05228/

As observed by Konus-Wind, the burst
had the total fluence of 1.97(-0.11,+0.11)x10^-4 erg/cm2,
and the 64-ms peak flux, measured from T0+38.848 s,
of 2.03(-0.19,+0.19)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+112.640 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 = -0.82(-0.05,+0.05),
the high energy photon index beta = -2.13(-0.10,+0.08),
the peak energy Ep = 590(-44,+47) keV
(chi2 = 83/97 dof).

The spectrum near the maximum count rate
(measured from T0+37.120 to T0+38.912 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 = -0.66(-0.05,+0.06),
the high energy photon index beta = -2.58(-0.27,+0.18),
the peak energy Ep = 753(-64,+68) keV
(chi2 = 61/66 dof).

Assuming the redshift z=3.270 (Cotter et al., GCN 46081)
and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315,
and Omega_Lambda = 0.685 (Planck Collaboration, 2014),
we estimate the following rest-frame parameters:
the isotropic energy release E_iso is  4.56(-0.25,+0.25)x10^54 erg,
the peak luminosity L_iso is 2.03(-0.19,+0.19)x10^54 erg/s,
the rest-frame peak energy of the time-averaged spectrum
Ep,i,z is 2518(-188,+199) keV and the spectrum near the maximum count rate
Ep,p,z is 3217(-272,+291) keV.

With the obtained estimates, GRB 261029A is inside 68% prediction bands for
both the 'Amati' and the 'Yonetoku' relations derived for the sample of >300 long
KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021),
see http://www.ioffe.ru/LEA/GRBs/GRB261029_T05228/GRB261029A_rest_frame.pdf

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