GCN Circular 44585
Subject
Konus-Wind detection of GRB 260511A
Event
Date
2026-05-12T16:55:02Z (5 months ago)
From
Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>
Via
Web form
A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
The long-duration GRB 260511A
(Fermi-GBM detection: Fermi GBM team, GCN 44529;
Roberts et al., GCN 44548;
BALROG localization: Preis & Greiner, GCN 44531;
SVOM detection: Godet et al., GCN 44532;
NuSTAR detection: Waratkar et al., GCN 44555)
triggered Konus-Wind at T0=22416.401 s UT (06:13:36.401).
The burst light curve shows a multipeaked structure
which starts at ~T0-4.6 s and has a total duration of ~20.5 s.
The emission is seen up to ~6 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260511_T22416/
As observed by Konus-Wind, the burst
had a fluence of 1.72(-0.05,+0.05)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+0.482 s,
of 6.96(-0.71,+0.71)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 = -0.79(-0.08,+0.09)
and Ep = 187(-8,+8) keV (chi2 = 107/99 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.1
(chi2 = 107/98 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:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.66(-0.08,+0.08)
and Ep = 187(-6,+7) keV (chi2 = 88/86 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.9
(chi2 = 87/85 dof).
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.