GCN Circular 44647

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

A long-duration GRB 260515A (SVOM detection: Brunet et al., GCN 44622
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was detected by Konus-Wind (KW)in the waiting mode at T0=T0(KW)~19:08:19UT.
A Bayesian block analysis of the KW data in the 20-1500 keV
band reveals a ~8 sigma count rate increase in the interval
from ~T0+0.4 s to ~T0+9.3 s from the SVOM detection time.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260515A/

Modeling the time-integrated spectrum of the burst
by a power law with exponential cutoff (CPL) model
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha = -1.37 (-0.17, + 0.17) and Ep = 95(-9,+10) keV.
In the 10 keV -10 MeV band, standard for the KW analysis,
the burst fluence is (7.70 ± 0.81)x10^-6 erg/cm^2
and the 2.944 s peak energy flux is (1.47 ± 0.22)x10^-7 erg/cm^2/s.

Assuming the redshift z=0.764 (Malesani et al., GCN 44629
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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 burst isotropic energy release E_iso to (1.25 ± 0.15)x10^52 erg,
the isotropic peak luminosity L_iso to (5.70 ± 0.85)x10^50 erg/s, and
the rest-frame peak spectral energy Ep,z to (168 ± 18) keV.
With the obtained estimates, GRB 260515A is consistent with 68% prediction bands
of both 'Amati' relation and 90% prediction bands of 'Yonetoku' relation 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/GRB260515A/GRB260515A_rest_frame.pdf

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