TITLE:   GCN CIRCULAR
NUMBER:  44332
SUBJECT: Konus-Wind detection of GRB 260411B
DATE:    26/04/17 17:11:27 GMT
FROM:    Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>

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 260411B
(Fermi-GBM detection: The Fermi GBM team, GCN 44262,
Pathak & Sonawane, GCN 44266;
BALROG localization: Preis & Greiner, GCN 44263;
SVOM-GRM detection: Wang et al., GCN 44268;
Fermi-LAT detection: Longo et al., GCN 44277;
GECAM-B detection: Zao et al., GCN 44285;
Glowbug detection: Woolf et al., GCN 44312;
IPN triangulation: Kozyrev et al., GCN 44329) 
triggered Konus-Wind at T0=29079.388 s UT (08:04:39.388).

The burst light curve shows a multipeaked structure
which starts at ~T0-8.7 s and has a total duration of ~55.6 s.
The emission is seen up to ~10 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260411_T29079/

As observed by Konus-Wind, the burst
had a fluence of 4.50(-0.50,+0.50)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+1.440 s,
of 1.15(-0.14,+0.14)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+49.408 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 = -0.62(-0.18,+0.19),
the high energy photon index beta = -2.12(-0.19,+0.12),
the peak energy Ep = 290(-38,+52) keV
(chi2 = 82/98 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 the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.16(-0.15,+0.16),
the high energy photon index beta = -2.19(-0.10,+0.08),
the peak energy Ep = 248(-19,+23) keV
(chi2 = 87/82 dof).

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