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GCN Circular 33509

Subject
Konus-Wind detection of GRB 230304B
Date
2023-03-23T13:08:58Z (a year ago)
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 long-duration GRB 230304B
(Fermi-GBM detection: the Fermi GBM team, GCN Circ. 33396;
GRBAlpha detection: Dafcikova et al., GCN Circ. 33398;
AstroSat-CZTI detection: Navaneeth et al., GCN Circ. 33400;
CALET-GBM detection: Kobayashi et al., GCN Circ. 33423;
IPN triangulation: Kozyrev et al., GCN Circ. 33480)
triggered Konus-Wind at T0=52553.382 s UT (14:35:53.382).

The burst light curve shows a multi-peaked structure
which starts at ~T0 and has a total duration of ~53 s.
The emission is seen up to ~6 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB230304_T52553/

As observed by Konus-Wind, the burst
had a fluence of 4.57(-0.41,+0.60)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+0.560 s,
of 1.21(-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+40.448 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 = -1.05(-0.09,+0.09),
the high energy photon index beta = -3.34(-6.66,+0.68),
the peak energy Ep = 299(-28,+32) keV
(chi2 = 68/82 dof).

The spectrum near the maximum count rate
(measured from T0 to T0+7.680 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.89(-0.08,+0.09)
and Ep = 352(-27,+31) keV (chi2 = 91/83 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.2
(chi2 = 91/82 dof).

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