[vsnet-grb-info 18557] Konus-Wind observation of GRB 161004B

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20005
SUBJECT: Konus-Wind observation of GRB 161004B
DATE:    16/10/06 16:02:46 GMT
FROM:    Anastasia Tsvetkova at Ioffe Institute  <tsvetkova at mail.ioffe.ru>

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

The long-duration GRB 161004B (Swift-BAT trigger #715246:
D'Ai et al., GCN 19987; Sakamoto et al., GCN 19995;
Fermi GBM detection: Hamburg & Meegan, GCN 19998;
CALET Gamma-Ray Burst Monitor detection: Yamada et al., GCN 20003)
triggered Konus-Wind at T0=83274.317 s UT (23:07:54.317).

The burst light curve shows a single pulse with a total duration of ~18 s.
The emission is seen up to ~2 MeV.

As observed by Konus-Wind, the burst
had a fluence of 1.71(-0.07,+0.08)x10^-5 erg/cm2,
and a 64-ms peak energy flux, measured from T0+4.144 s,
of 3.43(-0.80,+0.80)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst
(measured from T0 to T0+15.616 s)
is best fit in the 20 keV - 2 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -1.05(-0.09,+0.09),
and Ep = 175(-12,+14) keV (chi2 = 56/58 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index:
beta < -3.14 (chi2 = 56/57 dof).

The spectrum near the peak count rate
(measured from T0 to T0+7.424 s)
is best fit in the 20 keV - 2 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.71(-0.10,+0.11),
and Ep = 210(-13,+15) keV (chi2 = 67/58 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index:
beta < -3.12 (chi2 = 67/57 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB161004_T83274/

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