TITLE:   GCN CIRCULAR
NUMBER:  29664
SUBJECT: Konus-Wind detection of GRB 210318B
DATE:    21/03/18 17:27:52 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 210318B
(Swift-BAT detection: Troja et al., GCN Circ. 29663)
triggered Konus-Wind at T0=11309.57 s UT (03:08:29.570).

The burst light curve shows a multipeaked structure
which starts at ~T0-0.5 s and has a total duration of ~14 s.
The emission is seen up to ~3 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB210318_T11309/

As observed by Konus-Wind, the burst
had a fluence of 3.83(-0.44,+0.50)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+1.872 s,
of 1.57(-0.28,+0.29)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+13.824 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 = -0.81(-0.12,+0.15),
the high energy photon index beta = -2.51(-0.39,+0.23),
the peak energy Ep = 264(-32,+33) keV
(chi2 = 70/82 dof).

The spectrum near the maximum count rate
(measured from T0+0.256 to T0+5.632 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 = -0.64(-0.13,+0.14),
the high energy photon index beta = -2.59(-0.45,+0.23),
the peak energy Ep = 297(-32,+36) keV
(chi2 = 67/81 dof).

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