GCN Circular 16854

S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik,
M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration, intense GRB 140928A (Fermi-LAT detection: Desiante et 
al., GCN 16847
Not found
 
 
;
Fermi-GBM detection: von Kienlin and Meegan, GCN 16850
Not found
 
 
;
IPN triangulation: Hurley et al., GCN 16852
Not found
 
 
)
triggered Konus-Wind at T0=37793.602 s UT (10:29:53.602).

The burst light curve shows two emission episodes with a total duration 
of ~69 s.
The first emission episode lasts from ~T0-6 s to ~T0+15 s
and the second episode lasts from ~T0+42 s to ~T0+63 s
(Fermi-GBM missed the second episode probably due to the Earth occultation).
The IPN data confirm the second episode belongs to the same GRB.
The emission is seen up to ~15 MeV.

As observed by Konus-Wind, the burst
had a fluence of 8.6(-1.4,+1.3)x10^-5 erg/cm2,
and a 64-ms peak energy flux, measured from T0+9.248 s,
of 1.7(-0.3,+0.3)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+57.856 s)
is best fit in the 20 keV - 10 MeV range
by a GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.17(-0.09,+0.12),
the high energy photon index beta = -2.09(-0.32,+0.16),
the peak energy Ep = 304(-66,+80) keV,
chi2 = 73/84 dof.

The spectrum near the peak count rate
(measured from T0+6.912 to T0+16.896 s)
is best fit in the 20 keV - 15 MeV range
by a GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.11(-0.08,+0.09),
the high energy photon index beta = -2.27(-0.34,+0.17),
the peak energy Ep = 318(-46,+59) keV,
chi2 = 84/93 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB140928_T37793/

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