[vsnet-grb-info 21155] Konus-Wind observation of GRB 180914A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23254
SUBJECT: Konus-Wind observation of GRB 180914A
DATE:    18/09/18 15:46:59 GMT
FROM:    Anastasia Tsvetkova at Ioffe Institute  <tsvetkova at mail.ioffe.ru>

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

The long GRB 180914A (Fermi-LAT detection:
Bissaldi, Kocevski & Omodei , GCN 23225;
Fermi GBM detection: Poolakkil, Meegan & Bissaldi, GCN 23227;
IPN Triangulation: Hurley et al., GCN 23247;
AstroSat CZTI detection: Sharma at al., GCN 23248)
triggered Konus-Wind at T0=45119.268 s UT (12:31:59.268).

The burst light curve shows multiple pulses
in the interval from T0 - 11 s to T0+143 s.
A total duration of the burst (T100) is ~154 s.
The emission is seen up to ~20 MeV.

As observed by Konus-Wind, the burst
had a fluence of 9.08(-0.51,+0.57)x10^-5 erg/cm2,
and a 64-ms peak energy flux, measured from T0+13.408 s,
of 6.05(-1.28,+1.29)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+147.200 s)
is best fit in the 20 keV - 20 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.68(-0.12,+0.13),
and Ep = 301(-25,+30) keV (chi2 = 136/98 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index:
beta < -2.43 (chi2 = 134/97 dof).

The spectrum near the peak count rate
(measured from T0+7.936 to T0+16.128 s)
is best fit in the 20 keV - 20 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.51(-0.13,+0.14),
and Ep = 356(-31,+37) keV (chi2 = 112/98 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index:
beta < -2.82 (chi2 = 112/97 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180914_T45119/

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