TITLE:   GCN CIRCULAR
NUMBER:  29911
SUBJECT: Konus-Wind detection of GRB 210424B
DATE:    21/04/29 12:54:06 GMT
FROM:    Dmitry Svinkin at Ioffe Institute  <svinkin@mail.ioffe.ru>

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

The short-duration, very bright GRB 210424B
(IPN triangulation: Hurley et al., GCN Circ. 29909)
triggered Konus-Wind at T0=28916.081 s UT (08:01:56.081).

The burst light curve shows a multi-peaked structure
which starts at ~T0-0.1 s and has a total duration of ~1.6 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/GRB210424_T28916/

As observed by Konus-Wind, the burst
had a fluence of 8.91(-0.83,+0.93)x10^-6 erg/cm2,
and a 16-ms peak flux, measured from T0+0.800 s,
of 3.13(-0.52,+0.54)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+1.024 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.39(-0.17,+0.20),
the high energy photon index beta = -2.76(-0.45,+0.25),
the peak energy Ep = 198(-21,+23) keV
(chi2 = 62/55 dof).

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