[vsnet-grb-info 27539] Konus-Wind detection of GRB 210306A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29642
SUBJECT: Konus-Wind detection of GRB 210306A
DATE:    21/03/10 10:05:25 GMT
FROM:    Anna Ridnaia at Ioffe Institute  <ridnaia at mail.ioffe.ru>

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

The long-duration GRB 210306A
(Swift-BAT detection: D'Elia et al., GCN 29597, Laha et al., GCN 29617;
Fermi-LAT detection: Ohno et al., GCN 29602;
Fermi-GBM observation: Veres, GCN 29605)
triggered Konus-Wind at T0=14040.731 s UT (03:54:00.731).

The burst light curve shows a multi-peaked emission complex,
which starts at ~T0-0.2 s and has a total duration of ~11 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/GRB210306_T14040/

As observed by Konus-Wind, the burst
had a fluence of 7.01(-0.45,+0.48)x10^-6 erg/cm2,
and a 64-ms peak flux, measured from T0+7.648 s,
of 3.99(-0.60,+0.67)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+16.640 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 = -1.21(-0.20,+0.22)
and Ep = 77(-7,+7) keV (chi2 = 48/49 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.6
(chi2 = 46/48 dof).

The spectrum near the peak count rate
(measured from T0+0.256 to T0+8.448 s)
is best fit in the 20 keV - 1 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.17(-0.23,+0.30),
the high energy photon index beta = -2.97(-1.31,+0.34),
the peak energy Ep = 70(-7,+7) keV
(chi2 = 56/49 dof).

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