TITLE:   GCN CIRCULAR
NUMBER:  44967
SUBJECT: Konus-Wind detection of GRB 260616A
DATE:    26/06/17 15:37:03 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 260616A
(Fermi-GBM detection: Fermi GBM team, GCN 44948;
BALROG localization: Preis & Greiner, GCN 44949;
Fermi-LAT detection: Lopez et al., GCN 44960;
GECAM-B detection: Guo et al., GCN 44964)
triggered Konus-Wind at T0=12085.625 s UT (03:21:25.625).

The burst light curve shows a bright, multipeaked pulse,
which starts at ~T0-63 s and has a total duration of ~292 s.
A weaker possible precursor is clearly visible in the KW waiting mode
data around ~T0-422 s. The emission is seen up to ~4 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260616_T12085/

As observed by Konus-Wind, the burst
had the total fluence of 2.77(-0.09,+0.09)x10^-4 erg/cm2,
and the 64-ms peak flux, measured from T0+82.880 s,
of 7.35(-1.24,+1.23)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+105.984 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 = -0.76(-0.03,+0.04),
the high energy photon index beta = -2.28(-0.06,+0.05),
the peak energy Ep = 295(-10,+11) keV
(chi2 = 118/97 dof).

The spectrum near the maximum count rate
(measured from T0+81.408 to T0+89.600 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 = -0.97(-0.08,+0.09),
the high energy photon index beta = -2.23(-0.25,+0.15),
the peak energy Ep = 379(-49,+57) keV
(chi2 = 87/87 dof).

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