[vsnet-grb-info 20820] Konus-Wind observation of GRB 180704A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22918
SUBJECT: Konus-Wind observation of GRB 180704A
DATE:    18/07/06 16:06:15 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred at mail.ioffe.ru>

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

The long GRB 180704A (Swift/BAT detection: Sonbas et al.,
GCN 22885; Markwardt et al., GCN 22894;
AstroSat CZTI detection: Sharma et al., GCN 22901)
triggered Konus-Wind at T0=20182.254 s UT (05:36:22.254).

The KW light curve shows a multi-peaked structure with
a total duration of ~40 s. A possible precursor is
seen in the waiting mode data around T0 - 62 s.
The emission is seen up to ~4 MeV.

As observed by Konus-Wind, the burst had a fluence of
(1.8 ± 0.1)x10^-5 erg/cm2 and a 64-ms peak energy flux,
measured from T0+20.352, of (2.4 ± 0.2)x10^-6 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+24.832 s)
is best fit in the 20 keV - 15 MeV range by a cutoff power-law
(CPL) function with the following model parameters:
the photon index alpha = -0.49(-0.13,+0.14),
and the peak energy Ep = 183(-11,+33) keV,
chi2 = 98/98 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep, and only an upper limit on beta (<-3.2).

The spectrum near the peak count rate (measured from T0+16.640
to T0+24.832 s) is best fit in the 20 keV - 15 MeV range by
the CPL function with the following model parameters:
the photon index alpha = -0.38(-0.20,+0.22),
and the peak energy Ep = 163(-13,+15) keV,
chi2 = 121/98 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep, and only an upper limit on beta (<-3.2).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180704_T20182/

All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.