TITLE:   GCN CIRCULAR
NUMBER:  33427
SUBJECT: Konus-Wind detection of GRB 230307A
DATE:    23/03/08 21:50:47 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 very intense, long-duration GRB 230307A
(Fermi-GBM detection: the Fermi GBM team, GCN Circ. 33405;
Dalessi, GCN Circ. 33407; Dalessi and Roberts, GCN Circ. 33411;
GECAM detection: Xiong et al., GCN Circ. 33406;
Solar Orbiter STIX detection: Xiao and Krucker, GCN Circ. 33410;
AGILE-MCAL detection: Casentini et al., GCN Circ. 33412;
IPN triangulation: Kozyrev et al., GCN Circ. 33413 and 33425;
AstroSat CZTI detection: Navaneeth et al., GCN Circ. 33415;
GRBAlpha detection: Dafcikova et al., GCN Circ. 33418;
VZLUSAT-2 detection: Ripa et al., GCN Circ. 33424)
triggered Konus-Wind at T0=56645.615 s UT (15:44:05.615).

The burst light curve shows a multipeaked structure
which starts at ~T0 and has a total duration of ~196 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/GRB230307_T56645/

As observed by Konus-Wind, the burst
had a fluence of 3.58(-0.08,+0.08)x10^-3 erg/cm2,
and a 64-ms peak flux, measured from T0+6.224 s,
of 6.66(-0.42,+0.46)x10^-4 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+71.424 s)
is best fit in the 530 keV - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.60(-0.08,+0.08)
and Ep = 1000(-16,+15) keV (chi2 = 41/42 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -5.4
(chi2 = 41/41 dof).

The spectrum near the maximum count rate
(measured from T0+6.144 to T0+6.400 s)
is best fit in the 530 keV - 10 MeV range
by a power law with exponential cutoff model:
with  alpha = -0.13(-0.31,+0.35)
and Ep = 1321(-62,+60) keV (chi2 = 19/21 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -4.3
(chi2 = 19/20 dof).

The energy fluence of the burst is the second highest
(after BOAT GRB 221009A) and the energy peak flux is the 5th highest 
observed for GRBs for almost 28 years of the KW operation.
This supports the results reported in Burns et al., GCN Circ. 33414.

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