TITLE:   GCN CIRCULAR
NUMBER:  24730
SUBJECT: Konus-Wind observation of GRB 190531B
DATE:    19/06/03 17:52:24 GMT
FROM:    Dmitry Svinkin at Ioffe Institute  <svinkin@mail.ioffe.ru>

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

The long-duration GRB 190531B
(Fermi-GBM detection: The Fermi GBM team, GCN Circ. 24695;
Fermi-GBM observations: Veres and Meegan, GCN Circ. 24705;
Fermi-LAT detection: Axelsson et al., GCN Circ. 24701;
Insight-HXMT/HE detection: Yi et al., GCN Circ. 24713)
triggered Konus-Wind at T0=72616.175 s UT (20:10:16.175).

The burst light curve shows a multipeaked structure
which starts at ~T0-38 s and has a total duration of ~110 s.
The emission is seen up to ~5 MeV.

As observed by Konus-Wind, the burst
had a fluence of 1.51(-0.15,+0.16)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+17.648 s,
of 1.96(-0.30,+0.30)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+83.712 s)
is best fit in the 20 keV - 5 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.73(-0.08,+0.08),
the high energy photon index beta = -2.25(-0.21,+0.14),
the peak energy Ep = 364(-34,+40) keV
(chi2 = 63/72 dof).

The spectrum near the maximum count rate
(measured from T0+15.616 to T0+19.456 s)
is best fit in the 20 keV - 7 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.60(-0.08,+0.09),
the high energy photon index beta = -2.64(-0.46,+0.26),
the peak energy Ep = 520(-53,+55) keV
(chi2 = 87/77 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB190531_T72616/

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