TITLE:   GCN CIRCULAR
NUMBER:  27581
SUBJECT: Konus-Wind observation of GRB 200412B
DATE:    20/04/15 09:16:05 GMT
FROM:    Anna Ridnaia at Ioffe Institute  <ridnaia@mail.ioffe.ru>

A. Ridnaia, S. Golenetskii, R. Aptekar, 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 200412B
(Fermi-GBM detection: The Fermi GBM team, GCN Circ. 27547;
Mailyan and Hamburg, GCN Circ. 27558;
BALROG localization: Burgess et al., GCN Circ. 27548;
Fermi-LAT detection: Longo et al., GCN Circ. 27557;
AstoSat CZTI detection: Gupta et al., GCN Circ. 27563;
Insight-HXMT/HE detection: Zheng et al., GCN Circ. 27565;
CALET-GRBM detection: Tamura et al., GCN Circ. 27572)
triggered Konus-Wind at T0=32924.203 s UT (09:08:44.203).

The burst light curve shows a multipeaked structure
which starts at ~T0-0.5 s and has a total duration of ~30.5 s.
The emission is seen up to ~6 MeV.

As observed by Konus-Wind, the burst
had a fluence of 1.12(-0.05,+0.05)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+5.744 s,
of 5.12(-0.43,+0.44)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+15.360 s)
is best fit in the 20 keV - 6 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.67(-0.05,+0.05),
the high energy photon index beta = -2.45(-0.12,+0.10),
the peak energy Ep = 289(-16,+16) keV
(chi2 = 66/79 dof).

The spectrum near the maximum count rate
(measured from T0+5.376 to T0+5.888 s)
is best fit in the 20 keV - 6 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.15(-0.10,+0.11),
the high energy photon index beta = -2.58(-0.17,+0.14),
the peak energy Ep = 316(-24,+24) keV
(chi2 = 56/56 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB200412_T32924/

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