GCN Circular 26975

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

The long-duration, bright GRB 200131A
(Swift-BAT detection: Sbarufatti et al., GCN Circ. 26953
Not found
 
 
;
Sakamoto et al., GCN Circ. 26967
Not found
 
 
;
CALET Gamma-Ray Burst Monitor detection: Ricciarini et al., GCN 26972
Not found
 
 
)
triggered Konus-Wind at T0=81673.507 s UT (22:41:13.507).

The burst light curve shows a bright, multi-peaked structure
which starts at ~T0-0.1 s and has a duration of ~3 s,
followed by a weaker episode at ~T0+32 s.
The emission is seen up to ~4 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB200131_T81673/

As observed by Konus-Wind, the burst
had a fluence of 1.60(-0.08,+0.09)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+0.068 s,
of 1.64(-0.27,+0.28)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The spectrum of the brightest episode
(measured from T0 to T0+9.984 s)
is best fit in the 20 keV - 4 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.80(-0.09,+0.10)
and Ep = 228(-15,+17) keV (chi2 = 43/72 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.2
(chi2 = 43/71 dof).

The spectrum near the maximum count rate
(measured from T0 to T0+0.256 s)
is best fit in the 20 keV - 4 MeV range
by a power law with exponential cutoff model:
with alpha = 0.01(-0.19,+0.21)
and Ep = 266(-22,+25) keV (chi2 = 49/38 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.8
(chi2 = 46/37 dof).

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