[vsnet-grb-info 16899] Konus-Wind observation of GRB 150819B

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18180
SUBJECT: Konus-Wind observation of GRB 150819B
DATE:    15/08/20 12:46:07 GMT
FROM:    Dmitry Svinkin at Ioffe Institute  <svinkin at mail.ioffe.ru>

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

The short-duration, very intense GRB 150819B
(IPN triangulation: Golenetskii et al., GCN 18176;
Fermi GBM detection: Yu and Burns, GCN 18178)
triggered Konus-Wind at T0=38000.750 s UT (10:33:20.750).

The burst light curve shows at least three separate peaks.
A total duration of the burst is  ~1.2 s.
The emission is seen up to ~3 MeV.

As observed by Konus-Wind, the burst
had a fluence of 6.61(-0.88,+1.10)x10^-6 erg/cm2,
and a 16-ms peak flux, measured from T0+0.008 s,
of 1.20(-0.17,+0.19)x10^-4 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 5 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -1.03(-0.21,+0.24)
and Ep = 348(-70,+116) keV (chi2 = 74/89 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index:
beta < -2.3 (chi2 = 74/88 dof).

The spectrum near the maximum count rate
(measured from T0 to T0+0.064 s)
is best fit in the 20 keV - 5 MeV range
by a power law with exponential cutoff model
with  alpha = -0.41(-0.15,+0.17)
and Ep = 618(-86,+95) keV (chi2 = 57/43 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index:
beta < -2.8 (chi2 = 57/42 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB150819_T38000/

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