TITLE:   GCN CIRCULAR
NUMBER:  44887
SUBJECT: Konus-Wind detection of GRB 260604C
DATE:    26/06/09 16:52:29 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 260604C
(Fermi-GBM detection: Fermi GBM team, GCN 44822,
Neights et al., GCN 44831;
SVOM-ECLAIRs detection: Gotz et al., GCN 44823,
Brunet et al., GCN 44883;
GECAM-B detection: Luo et al., GCN 44854;
AstroSat-CZTI detection: Arya et al., GCN 44885)
triggered Konus-Wind at T0=73128.568 s UT (20:18:48.568).

The burst light curve shows a single pulse
which starts at ~T0-3.2 s and has a duration of ~8.5 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/GRB260604_T73128/

As observed by Konus-Wind, the burst
had the total fluence of 3.60(-0.26,+0.26)x10^-5 erg/cm2,
and the 64-ms peak flux, measured from T0+3.056 s,
of 2.25(-0.18,+0.18)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+12.032 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 = -0.92(-0.05,+0.06),
the high energy photon index beta = -2.33(-0.19,+0.13),
the peak energy Ep = 421(-37,+40) keV
(chi2 = 82/89 dof).

The spectrum near the maximum count rate
(measured from T0+0.256 to T0+3.840 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 = -0.73(-0.06,+0.06),
the high energy photon index beta = -2.07(-0.07,+0.06),
the peak energy Ep = 374(-32,+35) keV
(chi2 = 60/71 dof).

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