GCN Circular 37927

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

The long-duration GRB 241025A
(Swift-BAT detection: Ambrosi et al., GCN 37859
Not found
 
 
;
Fermi-GBM detection: Fermi GBM team, GCN 37860
Not found
 
 
;
Godwin, GCN 37886
Not found
 
 
;
SVOM-GRM detection: Wang et al., GCN 37863
Not found
 
 
;
EP-WXT detection: Li et al., GCN 37864
Not found
 
 
)
was detected by Konus-Wind (KW) in the waiting mode
at T0~5786 s UT (01:36:26).

A Bayesian block analysis of the KW  waiting mode data
in the 20-300 keV band reveals a >20 sigma count rate
increase in the interval from T0-13 s to ~T0+128 s.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB241025A/

The total burst fluence is 1.58(-0.14,+0.14)x10^-5 erg/cm^2,
and the 2.944 s peak energy flux, measured from T0+0.143 s,
is 4.5(-0.5,+0.5)x10^-7 erg/cm^2.
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst,
measured from T0-13 s to T0+128 s,
can be described by a power law with exponential cutoff (CPL) model
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.85(-0.13,+0.15) and Ep = 238(-33,+38) keV.

The spectrum near the peak count rate, measured from T0+12 s to T0+30 s,
can be described by a CPL model with
alpha = -0.04(-0.17,+0.20) and Ep = 261(-23,+24) keV.

Assuming the redshift z=4.20 (Xu et al., GCN 37866
Not found
 
 
)
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 (5.5+/-0.5)x10^53 erg,
the peak luminosity L_iso is (8.2+/-0.9)x10^52 erg/s,
the rest-frame peak energy of the time-averaged spectrum
Ep,i,z is (1238+/-182) keV, and the spectrum near the maximum count rate 
Ep,p,z is (1357+/-120) keV.

With the obtained estimates, GRB 241025A is inside 68% prediction bands for 
'Amati' and 'Yonetoku' relations 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/GRB241025A/GRB241025A_rest_frame.pdf

All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.