[vsnet-grb-info 19810] Konus-Wind observation of GRB 170904A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21852
SUBJECT: Konus-Wind observation of GRB 170904A
DATE:    17/09/08 15:12:36 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, hard-spectrum, bright GRB 170904A
(IPN Triangulation: Hurley et al., GCN 21820)
triggered Konus-Wind at T0=35162.28 s UT (09:46:02.280).

The burst light curve shows multiple emission pulses
in the interval from ~T0-56 s ~T0+30 s.
The emission is seen up to ~19 MeV.
Weak count rate increases are seen in the same S1 KW detector
at ~T0-560 s and ~T0-350 s, however their attribution to this
GRB is unclear.

As observed by Konus-Wind, the burst
had a fluence of 1.73(-0.09,+0.09)x10^-4 erg/cm2,
and a 64-ms peak energy flux, measured from T0+11.728 s,
of 1.90(-0.32,+0.32)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst
(measured from T0 to T0+22.016 s)
is best fit in the 20 keV - 19 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.69(-0.05,+0.06),
the high energy photon index beta = -2.17(-0.10,+0.08),
the peak energy Ep = 466(-36,+40) keV,
chi2 = 115/97 dof.

The spectrum near the peak count rate
(measured from T0+9.984 to T0+11.776 s)
is best fit in the 20 keV - 19 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.73(-0.11,+0.13),
the high energy photon index beta = -2.19(-0.24,+0.15),
the peak energy Ep = 441(-72,+87) keV,
chi2 = 53/67 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170904_T35162/

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