GCN 45242: Konus-Wind detection of GRB 260727A

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

The long-duration GRB 260727A
(SVOM-ECLAIRs detection: Li et al., GCN 45220;
AstroSat-CZTI detection: Harsha et al., GCN 45225;
Glowbug detection: Cheung et al., GCN 45233)
triggered Konus-Wind at T0=1327.631 s UT (00:22:07.631).

The burst light curve shows a multi-peaked structure
which starts at ~T0-11 s and has a total duration of ~30 s (75-1200 keV).
The emission is seen up to ~300 keV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260727_T01327/

As observed by Konus-Wind, the burst
had the total fluence of 1.15(-0.03,+0.03)x10^-5 erg/cm2,
and the 64-ms peak flux, measured from T0+1.072 s,
of 1.61(-0.30,+0.30)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 = -0.20(-0.11,+0.11)
and Ep = 85(-2,+2) keV (chi2 = 107/98 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -4.2
(chi2 = 107/97 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:
with alpha = 0.02(-0.14,+0.14)
and Ep = 93(-3,+3) keV (chi2 = 80/82 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.8
(chi2 = 80/81 dof).

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