TITLE:   GCN CIRCULAR
NUMBER:  39619
SUBJECT: Konus-Wind detection of GRB 250306A
DATE:    25/03/07 22:30:19 GMT
FROM:    Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>

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

The long-duration GRB 250306A
(Swift-BAT detection: Evans et al., GCN 39606;
Astrosat-CZTI detection: Tembhurnikar et al., GCN 39611)
triggered Konus-Wind at T0=59404.612 s UT (16:30:04.612).

The burst light curve shows a double-peaked structure
which starts at ~T0-0.5 s and has a total duration of ~15 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/GRB250306_T59404/

As observed by Konus-Wind, the burst
had a fluence of 2.32(-0.15,+0.16)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+1.120 s,
of 1.40(-0.12,+0.12)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+18.176 s)
is best fit in the 20 keV - 20 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.94(-0.08,+0.08),
the high energy photon index beta = -2.78(-0.33,+0.19),
the peak energy Ep = 179(-10,+11) keV
(chi2 = 84/97 dof).

The spectrum near the maximum count rate
(measured from T0+0.256 to T0+1.792 s)
is best fit in the 20 keV - 20 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.62(-0.08,+0.09),
the high energy photon index beta = -2.59(-0.13,+0.10),
the peak energy Ep = 217(-13,+14) keV
(chi2 = 55/54 dof).

All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.