TITLE:   GCN CIRCULAR
NUMBER:  31907
SUBJECT: Konus-Wind detection of GRB 220403C
DATE:    22/04/15 20:20:51 GMT
FROM:    Dmitry Svinkin at Ioffe Institute  <svinkin@mail.ioffe.ru>

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

The bright, long-duration GRB 220403C
(Swift/BAT-GUANO detection: Tohuvavohu et. al, GCN Circ. 31824;
IPN triangulation: Kozyrev et al., GCN Circ. 31877)
triggered Konus-Wind at T0=36829.998 s UT (10:13:49.998).

The burst light curve shows multipeaked structure
which starts at ~T0-3 s and has a total duration of ~66 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/GRB220403_T36829/

As observed by Konus-Wind, the burst
had a fluence of 1.45(-0.20,+0.17)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+3.456 s,
of 2.81(-0.48,+0.47)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+64.512 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 = -1.12(-0.09,+0.10),
the high energy photon index beta = -1.86(-0.25,+0.11),
the peak energy Ep = 540(-130,+254) keV
(chi2 = 86/82 dof).

The spectrum near the maximum count rate
(measured from T0+3.328 to T0+4.096 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 = -0.86(-0.09,+0.11),
the high energy photon index beta = -2.38(-0.97,+0.31),
the peak energy Ep = 835(-200,+240) keV
(chi2 = 60/56 dof).

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.