TITLE:   GCN CIRCULAR
NUMBER:  25974
SUBJECT: Konus-Wind observation of GRB 191004B
DATE:    19/10/07 18:00:56 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 191004B
(Swift-BAT detection: Cenko et al., GCN circ. 25947;
Stamatikos et al., GCN circ. 25955)
triggered Konus-Wind at T0=77626.99 s UT (21:33:46.990).

The burst light curve shows a multi-peaked structure
which starts at ~T0-0.5 s and has a total duration of ~5.5 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/GRB191004_T77626/

As observed by Konus-Wind, the burst
had a fluence of 4.13(-0.40,+0.45)x10^-6 erg/cm2,
and a 64-ms peak flux, measured from T0+3.504 s,
of 2.56(-0.73,+0.74)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+8.448 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.51(-0.30,+0.34)
and Ep = 172(-21,+27) keV (chi2 = 59/57 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.0
(chi2 = 59/56 dof).

Assuming the redshift z=1.260 (D'Elia et al., GCN circ. 25956)
and a standard cosmology model with H_0 = 67.3 km/s/Mpc,
Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014),
we estimate the following rest-frame parameters:
the isotropic energy release E_iso is 1.79(-0.17,+0.20)x10^52 erg,
the peak luminosity L_iso is 2.51(-0.72,+0.73)x10^52 erg/s,
and the rest-frame peak energy of the time-integrated spectrum,
Ep,i, is 389(-47,+61) keV.
With these energetics, the burst lies within the 90% prediction bands
for both 'Amati' and 'Yonetoku' relations built for the sample
of 138 long KW GRBs with known redshifts
(Tsvetkova et al., ApJ 850 161, 2017).

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