TITLE:   GCN CIRCULAR
NUMBER:  29643
SUBJECT: Konus-Wind detection of GRB 210308A
DATE:    21/03/10 12:11:00 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 long-duration GRB 210308A
(Swift-BAT detection: D'Elia et al., GCN Circ. 29619,
Palmer et al., GCN Circ. 29633;
Fermi-GBM detection: Lesage et al., GCN Circ. 29626)
triggered Konus-Wind at T0=23879.936 s UT (06:37:59.936).

The burst light curve shows a multi-peaked structure
which starts at ~T0-3.8 s and has a total duration of ~8.9 s.
The emission is seen up to ~1 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB210308_T23879/

As observed by Konus-Wind, the burst
had a fluence of 5.00(-0.48,+0.53)x10^-6 erg/cm2,
and a 64-ms peak flux, measured from T0+1.264 s,
of 3.36(-0.85,+0.87)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 1 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.73(-0.32,+0.38)
and Ep = 150(-19,+25) keV (chi2 = 49/55 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.7
(chi2 = 49/54 dof).

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