TITLE:   GCN CIRCULAR
NUMBER:  33674
SUBJECT: Konus-Wind detection of GRB 230418A
DATE:    23/04/22 16:32:46 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 short-duration GRB 230418A
(Fermi-GBM detection: Roberts et al., GCN Circ. 33652;
Swift/BAT-GUANO detection: Ronchini et al., GCN Circ. 33653;
AGILE detection: Panebianco et al., GCN Circ. 33656;
AstroSat-CZTI detection: Navaneeth et al., GCN Circ. 33657;
IPN triangulation: Kozyrev et al., GCN Circ. 33659)
triggered Konus-Wind at T0=76289.941 s UT (21:11:29.941).

The burst light curve shows a multi-peaked structure
which starts at ~T0 s and has a total duration of ~0.3 s.
The emission is seen up to ~2 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB230418_T76289/

As observed by Konus-Wind, the burst
had a fluence of 4.13(-0.64,+0.76)x10^-6 erg/cm2,
and a 16-ms peak flux, measured from T0+0.048 s,
of 3.84(-1.00,+1.10)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+0.192 s)
is best fit in the 20 keV - 2 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.52(-0.20,+0.23)
and Ep = 1071(-228,+335) keV (chi2 = 16/24 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -1.87
(chi2 = 16/23 dof).

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